Athena Tennos from Hayate the Combat Butler used to be a literal prisoner in her palace. Hayate's brother Ikusa rescued her. Then, he disappeared.
Treize from Gundam Wing is confined to a posh country estate after he protests the Romefeller Foundation's decision to use Mobile Dolls.
In the Frozen Teardrop novels we learn that Relena's great-aunt Sabrina was locked away in a suite of her family's mansion, with her pet cat as her only companion.
The makers of Code Geass R2 designed Nunnally's garden aboard the airship with this in mind. The garden is incredibly nice and well cared for, but it's also surrounded by a deep, empty moat, with only a single narrow bridge leading to the rest of the ship. Since Nunnally is blind and confined to a wheelchair, this makes it extremely difficult/dangerous for her to leave the garden without assistance.
Lelouch is also put in one of these at Ashford Academy. It's a nice school, and many of his friends are there, but in R2 he's constantly being monitored by government agents looking for signs that he's regained his lost memories and become the terrorist leader Zero again. However, once his memories are back thanks to C.C's sort-of Kiss of Life ... by using Blackmail, Mind Control, and emotional manipulation on the agents sent to watch him, he soon turns the Gilded Cage into the Gilded Base For His Terrorist Operations.
This was also the case for Empress Tianzi, who lived, well, like an empress in the Vermilion Forbidden City, but whose greatest desire was to leave and see the world. Luckily for her, she once spared a young officer from execution — and said officer, Li Xingke, swore to make Tianzi's wish come true. He succeeded.
The "greenhouse" Suu was kept in in Clover. It's quite beautiful, but Suu has to live in complete isolation from the rest of the world, as she is powerful enough to defeat the government officials, and they "don't want that power to fall into the wrong hands."
Rea in Sankarea. She is restricted from ever leaving her estate by her Over Protective Dad to where she is barely even allowed to go out to school to the point she sneaks off at night to scream into an abandon well of how she wish she wasn't born a Sanka. And when she starts to talk to a boy, her father even takes school away from her to be home schooled and orders that the boy she was hanging out with to be castrated. After this, she drinks a chemical that contains poisons plants in an attempt to kill herself. Though it instead did something else.
Invoked in Magic Knight Rayearth when Zagato tells the Magic Knights that Emeraude has to "spent her whole life locked up in a cage" as a result of being Pillar. As Pillar, Emeraude was the most powerful person in Cephiro- but she had no freedom, at least not to have what she wished for the most (to be with the one she loved, Zagato, that is). Later echoed by the Magic Knights when the invaders wanted to take over Cephiro- especially when Aska wanted to be beautiful, and is told "but for who?", since the Pillar could not fall in love with anyone, lest their thoughts and wishes won't be for Cephiro anymore and it will start falling apart around them.
In The Familiar of Zero, Luctiana kidnaps Saito and Tiffania and takes them to her home in an oasis. They are allowed to roam around the paradise. Since they are in the middle of a desert, they can't possibly leave without a dragon or vehicle to ride.
In Attack on Titan, this is Eren's opinion of the last human city. Most of humanity is content to live in the walls indefinitely but Eren repeatedly calls it a bird cage and is determined to see the outside world.
Deconstructed in the manga of Trigun, where a woman in this situation begs Wolfwood to free her and he is not inclined to help. He points out a starving bird and comments on how much it would like to have a life like hers. Since the setting is a Death World, freedom is not all it's cracked up to be.
When Sasuke is taken by Orochimaru, he is given better living conditions in Orochimaru's compound. Subverted in that Sasuke is not an unwilling prisoner.
Another Batman example — in Batman Incorporated, after Talia usurps Ra's Al Ghul's control of the League of Assassins and absorbs it into Leviathan, she has him locked up in a cell that, at the very least, is well stocked with books, a chess set, and has a panoramic view of the surrounding mountains. Ra's himself even says that it's not that bad.
The Adventures of Tintin and the Picaros has one of these disguised as a country hotel, which Captain Haddock and Calculus are sent to after they accept Tapioca's invitation. It has cameras and microphones hidden all over, and guards who refuse to let guests head into town without armed escort, supposedly to protect them from the Picaros.
Haddock: That young whippersnapper Tintin was right! The cage may be a gilded one... but we're well and truly behind bars!
In the Blake and Mortimer book Atlantis Mystery, the two main characters stumble upon the titular lost civilization and forced to remain there in order to keep The Masquerade. Despite not being allowed to leave, they are treated like guests of honor, are given very plush accommodations and seem to be adapting somewhat until they find themselves targeted by the Big Bad.
In Astro City, Infidel resides in such a place of his own design as part of an arrangement with his archenemy Samaritan. It's a literal palace, floating in another dimension, and due to his magic powers he wants for nothing — even female companionship, as he's constructed homunculi. However, he longs for true freedom and is constantly trying to find a way to bypass the Samaritan's security measures.
In With Strings Attached, during the peaceful chapter where John and Ringo sit on the edge of the cliff and talk, the following exchange takes place:
John: We're in a gilded cage, mate. All the magic in the world don't change that.
Ringo: There's a lot more gold on this cage than in some we've been in.
John: Oh, fuck, man, I know. Obviously it’s better than bein’ a slave without the magic. Just ask George! And I know everythin' in life’s a trade-off. We traded our private lives for money and success. That’s fine. We wanted that. We worked for that. The difference here is we didn’t ask for this. It was forced on us.
During the third story of the My Hostage Not Yours series, when Zim starts conquering Earth, he eventually relocates his base to an European palace (it's never specified which). The resident royal family is allowed to stay, with full access to the staff and palace (minus areas closed off for Zim and Gaz's personal use), but Zim makes it clear that they're not allowed to leave the palace grounds unless they intend to do so permanently.
Twice in Cadance Of Cloudsdale for Princess Cadance. Her first cage, a monastery in Reduit, is where she was kept for her her centuries-long childhood, though she never came to resent it due to being on the level of a preschooler the whole time. When Celestia takes her to Canterlot palace and she begins growing normally, Cadance learns to hate all the restrictions and constant watch placed on her to ensure her safety. However, when her attempt to escape goes horribly wrong, Celestia relents and allows her to see more of Equestria.
Films — Animated
In Disney's The Hunchback of Notre Dame, Esmeralda claims sanctuary in Notre Dame Cathedral, which fits the grandeur element of the trope, though perhaps not the 'comfort.' Frollo invokes this trope almost by name.
Frollo: You have chosen a magnificent prison - but it is a prison nonetheless. Set one foot outside, and you're mine.
When Belle trades herself in for her father in the Beast's captivity in Beauty and the Beast, she initially thinks that she'll be kept in the dungeons, but the Beast takes her to much better arrangements in a guest room. She has the Beast's entire servant staff waiting on her and almost the entire castle to herself — none of which conceals the fact that she is a prisoner.
Princess Jasmine, Aladdin. She considers the palace to be a prison because she isn't allowed to leave.
Films — Live-Action
In Dr. No, the first cell James Bond and Honey Ryder are put in is like a five star hotel.
In the movie Quills, Dr. Royer-Collard allows his young wife to decorate their home with whatever materials she likes, no matter how ornate or expensive they are...but instructs the architects to install doors that can only be locked from the outside. In his twisted mind, this apparently justifies his continued raping of a girl young enough to be his granddaughter every night.
In the movie The Promise, Duke Wuhan imprisons Qingcheng in a golden cage, keeping her locked away within the castle.
Henry of Ever After specifically calls the castle his gilded cage because his father is telling his that he has to marry and be king.
In a deleted scene in Sucker Punch, the High Roller buys Baby Doll from the brothel and he calls the room he puts her in a gilded cage.
In The Mouse That Roared, the Duchy of Grand Fenwick unexpectedly wins their war against America. A group of New York City policemen, as prisoners of war, are fed and boarded in the best of comfort, while an Army general, knowing his rights, doggedly insists on a regulation 8-by-10 foot cell and food on a regulation tin plate.
In Moulin Rouge!, it's clear that Satine sees the glamorous Moulin Rouge (of which she is the star) as her prison — not because she's physically prevented from leaving, but because her only other option is life as a common street prostitute, which would be infinitely worse.
In The Student Prince In Old Heidelberg, Crown Prince Karl Heinrich is stuck inside his castle, unable to play with the other boys, or later, to marry the pretty barmaid, because he has to be a prince. One scene shows Karl Heinrich as a child literally behind bars (the fence around the palace), watching regular kids playing ball outside.
In the Red Dwarf episode "Legion", the boys are held captive in luxurious "prison" suites tailored specifically to their respective tastes, so that a sophisticated being named Legion can perpetuate his own existence by feeding off their combined psychic energy.
In a third season episode of Night Gallery entitled "The Ring with the Red Velvet Ropes" newly crowned heavyweight boxing champ Jim Figg is abducted immediately following his winning bout and transported to a luxurious mansion in an alternate dimension. There he learns that he will be well treated but kept a prisoner until after he has fought the owner of the mansion (played by Chuck Conners) to determine who is the real champion of the universe. If he loses he will be transported back to Earth. If he wins he will replace Conners and gain the companionship of Joan Van Ark.
In the 1998 series Merlin, King Vortigern keeps Nimue in a gilded cage, to ensure that her father stays loyal to him.
In the Star Trek: The Original Series episode "I Mudd", the Enterprise crew and Mudd himself are confined to a planet where androids serve their every need while preventing them from leaving.
In an episode of Star Trek: Voyager, Janeway's Leonardo da Vinci holodeck program is "kidnapped" from the ship, and enlisted by Tau, an alien merchant, to design things for him. Janeway attempts to convince Leonardo she is freeing him from Tau's imprisonment. Leonardo, as an artist from Renaissance-era Italy, sees Tau as a wealthy patron with unlimited resources who lets him create to his heart's content, and insists "if this is a cage, it is a cage of gold!"
In the season 4 finale of Supernatural, Zachariah and the other angels detain Dean in one of these to keep him from getting himself killed since he's one of the only people suitable to host the Archangel Michael and to prevent him from stopping Lucifer's escape. It's a lavish and opulent room stocked with Dean's favorite beer and the best burgers he remembers eating from his childhood; the angels even offer him Ginger and Mary Ann from Gilligan's Island because Dean has always had a thing for them, but he passes. In a moment of helpless despair, Dean almost gives in and tries to drink one of the beers right before Castiel breaks him out.
In the Doctor Who episode "Army of Ghosts", Torchwood One treats the Doctor as a guest of honor and follow his advice in dealing with the current issue...but also keep armed guards on him at all times and inform him that due to his earlier encounter with Queen Victoria (Torchwood's founder), he is considered an "enemy of the state":
The Doctor: If I'm the enemy, does that mean I'm a prisoner?
Yvonne Hartman: Oh yes, but we'll make you perfectly comfortable.
The department store for Charles and Ella in the 1966 Stephen Sondheim teleplay musical Evening Primrose. Ella recognizes it more than he does, however.
The Royal Apartment Crichton is sequestered in after he kisses the princess in the "Look at the Princess" trilogy.
When Moya's crew get to Earth in season 4, they're given a waterfront mansion...completely cordoned off from the surrounding area and under constant surveillance and security. John's voiceover even notes "It's a cage - but at least it's a gilded one."
In season six of 24, this is where we find former US President Charles Logan, as his punishment for his day 5 activities: He'd assassinated a former president and a few others and committed assorted acts of terrorism.
In the Showtime original series The Borgias, when Cesare Borgia finally defeats and captures Caterina Sforza, her brings her as a prisoner to Rome in a literal gilded cage.
A Song of Ice and Fire, Sansa becomes a prisoner at King's Landing after her father commits treason. She still lives in luxury and is treated as a Lady, but she's at the mercy of the Lannisters and has to keep of a facade of still loving Joffrey and hating her family for being traitors.
Following the failed Greyjoy rebellion, Eddard Stark took the last surviving Greyjoy heir, Theon, back to Winterfell to be his ward. In theory, his father wouldn't act up again, knowing if he did his son would be killed. While Theon had all of the comforts and was essentially treated as one of the family, he was still a prisoner and reminded of it frequently.
This is frequently the case in Westeros where "fostering" another lord's offspring is a euphemism for "holding them hostage to make sure their parents behave."
When a plot to put Princess Myrcella Baratheon on the throne fails, the royal plotter, Arianne Martell, is put by her father in a room full of comforts - great food, fantasy counterpart chess - but servants who won't speak a word to her.
At the end of Jurassic Park, all the survivors are kept in a resort and questioned about what they saw at the park. It's stated that the Costa Rican government is very worried what could happen if word gets out, and that the two children would be the only ones allowed to leave.
Apparently they relented, because in The Lost World, Ian Malcolm is no longer confined and it's mentioned in passing that Dr. Sattler teaches in California. This is because they signed an agreement not to tell anybody about what happened.
In Wielding a Red Sword in Piers Anthony's Incarnations of Immortality series, Prince Pride and the Princess Rapture are kept in a lavish magical honeymoon suite, which they cannot leave. Their kingdoms wish them to marry for political reasons, but neither even knows, let alone likes the other.
In the 1632 series, several citizens from the United States of Europe go to London. They are housed in the Tower of London and treated well (for the times at least), but they cannot leave. The characters are imprisoned there for several books.
In Stephen King's Firestarter, the rooms Andy and Charlie are placed in when they are captured by The Shop are very comfortable, with good food and television, and are comparable to hotel suites. This is no comfort to the characters, and it is remarked that despite all the luxuries, 'a dog turd covered with frosting is not a wedding cake; it is simply a frosted dog turd.'
In Stephen King's The Dark Tower novel, the Breakers live in a lovely, idyllic 1950s-esque town called Blue Heaven. At a distance, it resembles a college town, with the latest in movies, holographic sex simulations, food and drink. Their every whim is catered to. However, it is set in Thunderclap, a highly radioactive, toxic environment and is surrounded by electric fences and armed guards who will shoot on sight. Almost all Breakers have grown completely used to their privileges and don't care their mission is destroy all of reality. They "get along to get along."
In the first Gor book the Big Bad has an actual gilded cage that he keeps one of his slaves in.
The space colony with criminal ties named Interchange serves this function in The Demon Princes. It's an institution designed to hold people who have been kidnapped and held for ransom until someone pays the ransom. Kirth Gersen, who ends up in there temporarily, notes that while it's very comfortable and there's no lack of things to do, the whole atmosphere is depressing as nobody really talks to anyone else. And, you know, they've all been kidnapped.
In The Horse and His Boy, when Prince Rabadash is captured, the narrator notes the day afterwards that from the way he was carrying on, one would think that he had been thrown into a cold, wet cell for the night and given no food or water, but actually he was held in a Gilded Cage.
More importantly, this trope was the fate that Aravis was running from. She was to be pawned off as a child bride to the Vizier Ahoshta Tarkaan, the second most powerful man in the whole kingdom, and would've been little more than a puppet wife locked in a luxurious palace. (Aravis's already married friend Lasaraleen is in a similar situation, though she doesn't seem to mind that much.) It was really not helped by how the one to blame for this situation was Aravis's Wicked Stepmother, who manipulated Aravis's dad to come up with the arrangement so she could get rid of a stepdaughter that she hated.
Sigmund Ausfaller is "invited" to be a permanent "guest" of the Hindmost in Destroyer of Worlds.
This is the entirety of the book Twenty Thousand Leagues Under the Sea. As magnificent as the adventure is, Captain Nemo is holding Professor Arronax and his companions captive to keep the secret of the Nautilus safe. Ned Land certainly doesn't forget it.
Scarlett of The Power of Five is put in one of these during the fourth book. She actually realizes almost immediately that she is in a prison. A superbly comfortable, incredibly expensive and luxurious prison, but a prison nonetheless. What she doesn't realize is that in this case, "the management" is the Legions of Hell in all but name.
Subverted in Tairen Soul.Vadim Maur has very nice-looking chambers for all his important Fey prisoners to stay in. The catch is that for the most dangerous ones, every inch of the room is threaded with the black metal Sel'dor, which Fey are weak to. Therefore, the Fey in these beautiful chambers are in almost constant pain.
In the Sword of Truth series, the prophet Nathan Rahl is kept in one of these by the Sisters of the Light, and given every comfort, except wine, because a drunken prophet is bad news. Later in the series, Nathan Rahl escapes, and his Mord-Sith servants capture the Prelate, the leader of the Sisters of the Light. He then has her thrown in a grimy prison cell, refuses her requests to see him with the same answers she had refused him with over the years ("I'm busy and can't be bothered to come down every time you clamor for me!"), and gives her all the wine she wants. Later, he shows up to meet with her, acts as if her prison cell is a Gilded Cage, and then makes a brief speech about how all prisons, regardless of how pretty or comfortable they are, are fundamentally the same.
The same is true, though to a lesser degree, of all wizards held for training by the Sisters of the Light. Every one is held by a Restraining Bolt that keeps them from moving too far away from the Palace, though with a leeway of at least several miles. And aside from a few hours of daily mandatory training, all trainees are given free reign of the city, with a nigh unlimited allowance to see to their comforts. The catch is that as they progress in their training, the students begin to lose more and more privileges as their magic becomes more dangerous. Thus, a vast majority of the trainees are spoiled Jerkasses who do the bare minimum of training in order to not be promoted past the allowances they've become accustomed to.
Rasselas, Prince of Abyssinia by Samuel Johnson opens with the title character kept in a valley like all the princes who do not succeed to the throne, in the lap of luxury so they don't want to leave. Except that Rasselas finds himself inexplicably miserable. His tutor tells him that if he knew how miserable life was outside, he would appreciate the valley. Rasselas takes it as a suggestion.
In the Wheel of Time, Morgase stays as a 'guest' of the Children of the Light for a time. A somewhat dark case, as despite the appearance of civility, the captors were employing Cold-Blooded Torture (albeit of a type designed not to leave lasting marks) in order to compel her to acquiesce to their political demands; it's almost certain that she was raped as well.
In Codex Alera, this is part of the backstory. A Luxury Prison Suite that later contains an important ambassador was originally made for a previous Emperor's favorite mistress, who was accused of treason and imprisoned there until, with the Emperor going and personally interrogating her at least once a week.
Also in Codex Alera, long after the vord overran Alera Imperia there was a pleasant little town which was more-or-less untouched. Given the state of Alera at the time, this qualifies nicely. The town is surrounded by guards and their captor imposes one more, minor requirement — everyone is made sterile. The conqueror generously extends this offer to everyone in Alera.
In The Shamer Chronicles, this is what Dina was kept in after she got captured by the Villain in the second book.
Murtagh was kept confined by the Varden in Eragon after refusing to submit to a Mind Probe. Eragon is very distressed by this, assuming him to be languishing in a cell somewhere. In fact he is very comfortable with his every need catered for, and considers imprisonment somewhat preferable to the treatment he would get from most of the Varden. Not so much in the film.
In Discworld, Vetinari has a special section of his palace set aside for an Expy of Da Vinci as well as a series of traps from preventing anyone from getting in or out. The twist is that he doesn't actually mind it, or even seem to realise he's imprisoned, since his particular cage is filled with enough paper and ink and bits of things to keep his mind occupied the whole time.
Vetinari seems to have this as something of a policy; he claims that you should never build a dungeon you wouldn't want to spend the night in because if you are overthrown the usurper will have you tossed in it. It's not exactly luxurious, but it is clean, airy, and free of any of the snakes and scorpions that his predecessor employed. There are rats, but only because Vetinari taught them how to eliminate the snakes and scorpions, and in gratitude they act as servants. There's also a hidden key and the door can be bolted only on the inside. The man really thought this through.
Again at the hands of Vetinari, Moist von Lipwig finds his new life as Postmaster General to be this. He can go where he wants and do what he pleases...but he's under the watchful eye of a parole officer. Said officer is a golem who never sleeps, never stops working, is almost indestructible, and can sense Moist's location wherever he goes. He may be able to move around, but Moist is all too aware that he's still a prisoner.
Sisterhood Series by Fern Michaels: Cross Roads reveals that Henry "Hank" Jellicoe put the Vigilantes and the Big Five into these to keep them divided and unable to disrupt his plans to set up an assassination attempt on President Martine Connor and step in to stop it and make sure the Pentagon keeps funding him and his organization Global Sercurities. Fortunately, the Vigilantes and the Big Five eventually realized that they were stuck in these, and got out of them. Deja Vu reveals that Jellicoe put a reporter named Virgil Anders in one, because Virgil was writing a book about Jellicoe titled "Man, Myth, Monster", and Jellicoe objected to the "monster" part.
The city of Axiom Nexus in Transformers: TransTech, to any "units of interest" with technology the TransTechs deem useful. Axiom Nexus isn't that bad if you can manage to find a good niche for yourself, especially compared to the wartorn universe you're likely from... but you're still not allowed to ever leave or see your loved ones you left behind ever again.
Aleksandr Solzhenitsyn's In the First Circle is set in a sharashka, the Club Fed-style encampments within The Gulag for scientists doing necessary work (See below under "Real Life"). Solzhenitsyn himself served out most of his eight-year sentence in one, due to his talent as a mathematician.
The training area for tributes. Luxurious quarters, beautiful clothes, five star cuisine, and a top-notch training facility to prepare you for your fight to the death. Simply divine. Katniss even says that it will be their "home/prison until the Games begin."
It's implied that the five-star housing of the victors is also like this. Once they've won the game, they're celebrities around Panem and are treated like it. However, the Capitol keeps a close eye on them, because they are now potentially influential celebrities.
The wealthier districts have better living conditions but more brutal and fanatical Peacekeepers. On the other hand, District 12 is one of the poorest districts, but the authorities are far more willing to turn a blind eye to things like poaching and black market trading, or at least until they get replaced by new troops during Catching Fire.
The Capitol itself could also be seen as this - for somewhere that is supposedly very privileged, we see several people willing to risk their lives to escape. The fact that Seneca Crane was executed for simply failing at his job implies at least a very restrictive society, where you're watched constantly and not toeing the line has terrible consequences. In Catching Fire, Effie actually says 'That sort of thinking...it's forbidden, Peeta. Absolutely.' when Peeta tries to hold the Gamemakers accountable for killing children by painting a picture of Rue's death which implies the Capitol citizens may not quite have the freedom Katniss assumes.
In Redeeming Love, Angel’s life as a prostitute looks pretty cushy—she has extravagant clothes and the luxury suite in the brothel, and it’s implied that her services are in such high demand that she makes significantly more money than virtually anyone else in the Gold Fever town—but it’s revealed that she has no access to any of her income, doesn’t own her fine possessions, and has no control over what she does, where she goes, or whom she talks to; she is intensely lonely and bitter.
In For Your Safety this is the fate of all of humanity, as the GroupMind removes all the humans to a incredibly comfortable ring world in orbit around the Earth. They're provided with every possibly luxury by an army of billions of 'morphs, but may never leave the Ring, since the Earth has now been designated a nature preserve.
The children's attic prison in Flowers in the Attic initially comes across as this when they are fed regularly and frequently given expensive presents. It becomes a nothing more than a cage, however, when their mother increasingly neglects.
Hotel California"You can check out any time you'd like/But you can never leave!"
Which was a metaphor for drug addiction and death.
The phrase is dropped in the opera of Voltaire's Candide: "Harsh necessity brought me to this gilded cage — born to higher things, here I droop my wings... Singing of a sorrow nothing can assuage." (But it turns out that Cunegonde rather likes her gilded cage a lot more than she lets on!)
"Luxury Cage" by Republica
Mythology and Religion
In response to a prophecy that his son would become a great religious leader or a great king (and preferring that he become the latter), the father of Siddhartha Guatama kept him in one of these. It didn't work.
In Hindu Mythology, Sita is kidnapped and held in the palace of Lanka (complete with attendants) by King Ravana, for a whole year. He tried to sleep with her, but as she was already Happily Married to Rama, she refused Ravana's advances.
Johanna from Sweeney Todd: The Demon Barber of Fleet Street is living in one contructed by her guardian, Judge Turpin. Fittingly, she gets a song about it called "Green Finch and Linnet Bird" with an obvious bird and cage theme, in which she laments her inability to be content with her comfortable prison.
Upon the Plane of Ysgard is the Gilded Hall, where those Sensates that seek the pleasure of gullet and loin can be found. They indulge these passions in earnest, never realizing that the doors of the hall never open and that there is no clear path back to the Civic Festhall. They are the unwanted Sensates, the ones that do not truly believe in the faction, but instead seek only pleasure for pleasure's sake. Are prisoners who do not realize they are such truly prisoners?
In Illusion of Gaia, Kara constantly tries to escape her father's castle before joining Will and leaving permanently. She even describes it as a "prison of silk and gold".
The opening narration of the Mage Origin in Dragon Age: Origins describes the Tower of the Circle of Magi as one of these. The mages get access to better and better quarters as they rise in rank, they have access to all of the resources a student of magic could ever desire, and they get all of their needs provided for them. The Tranquil even make use of their talent for alchemy to brew fine ale. Too bad they can't ever leave the Tower except on official Circle business unless they want to risk Death by Templar. The same Templars who never let them out of their sight — always watching. Some mages learn to appreciate the benefits and opportunities the Circle provides and come to accept their restricted lives. Others... don't.
The restrictions aren't incredibly harsh in the Ferelden Circle, at least. In Awakening you can run into a Circle mage doing research on alchemical plants, in the middle of nowhere without any kind of supervision, implicitly for weeks at a time.
Zevran considers being an Antivan Crow to be this.
In Dragon Age II the Kirkwall Circle of Magi has it even worse: not only are the Templars even stricter (verging on psychotic), but over the course of the game the "gilding" on their cage is gradually removed; apart from that rather nasty point in which Ser Alrik was implied to be making mages Tranquil so he could use them as sex slaves, the most spartan it got was in Act II, when mages aren't even permitted to leave their cells. The Circle is even housed in a former prison complex, so the gilding was somewhat limited to begin with.
Hyrule Castle is something like this for Princess Zelda in The Legend of Zelda: Twilight Princess. She's still in her lavish childhood home, the interior of which remains untouched by the scourge of Twilight, and although she seems to prefer to remain in her tower, there's nothing to suggest she can't visit other parts of the building as well. But she can't leave.
The titular village of St. Mystere in Professor Layton and the Curious Village exists entirely as a place of safety for Flora, the Baron's orphaned daughter, where Ridiculously Human Robot servants and attendants protect and care for her. It's a pretty neat place, with puzzle-dispensing robots and a private amusement park and an elaborate tower for her exclusive residence. But she can't leave it until a worthy guardian appears and solves the riddle of the Golden Apple.
After becoming the new King Of Town, Strong Bad is kept in the Of Town's castle under constant surveillance and (over)protection from the Homestarmy in Strong Badia the Free. Escaping takes the entire rest of the episode.
Pokémon Black and White: You find Victini in a nice, cozy bedroom in the basement of an island lighthouse, where it's been for the last 200 years. It's suggested that the family who bought the land built the room as a place for Victini to hide in so it would be safe from those who would exploit its powers. After the player catches it, everyone agrees that it's safer in your hands.
N's childhood room is another example. He grew up in a huge room, complete with a half-pipe... but that was the extent of his contact with the world until the events of the game.
The Lucky 38 Presidential Suite in Fallout: New Vegas, though only in the eyes of Cass, who is at nature a wastelander with little fondness for the lights of Vegas. The others range from ambivalent to (in the case of Veronica) enjoying living in a fancy Old World hotel.
The Sierra Madre Casino became this when its security systems activated during the nuclear war, trapping the Gala Event guests inside to either starve to death or be killed by the Security Holograms.
Vault 101 from Fallout 3 is another example. Providing you are willing to obey the Overseer, the dictator who runs the place, and never leave, life is dull but comfortable. Meanwhile, people in the wasteland outside are free but have to contend with raiders, mutants and fascist militias trying to kill them at every turn.
The vaults in general were advertised as this in the event of a nuclear apocalypse, however in reality most of them were designed as experiments and the majority who entered them often suffered rather unfortunate ends.
In Mass Effect 2, the Normandy SR-2 is one of these for Shepard; essentially created to make Shepard more comfortable while working with Cerberus, it's a replica of the first Normandy, but equipped with civilian luxuries that the original never had: a research lab, a kitchen, a lounge with observation windows and a mini-bar, and (as Joker points out) leather seats. Shepard's even given an upper deck for use as his/her private quarters, complete with a king-sized bed, an office space, an en-suite bathroom, a massive fishtank, and a display case for model ships. In spite of all these benefits, it's still a gilded cage: the entire ship has been bugged and most of the crew are loyal Cerberus operatives, so the Illusive Man is notified of whatever happens on-board; in spite of all the leeway Shepard is given, s/he's still firmly under the Illusive Man's thumb for most of the game.
Shepard: If we're stuck here, we might as well let them pamper us.
Joker: Does it breach uniform regs if I get that on a t-shirt? 'Cause this is my favourite "You Have No Choice" choice, ever.
Shepard: Technically, this is a civilian ship. I'm probably lucky you're still wearing pants.
Joker: Yeah, I'll save that for the off-hour cameras...
At the end of the game, you have the option to make off with it and get a chance for an immensely satisfying screw you to TIM.
A bird in a gilded cage is the manifestiation of Yukiko Amagi's shadow in Persona 4, representing her frustration at having already had her fate of inheriting her family inn decided for her and tying her down to Inabi for the rest of her life.
Wrathion of World of Warcraft claims this would have been his fate as the last black drake if he had not escaped the Red Dragonflight. He would have been effectively imprisoned inside Wyrmrest Accord and kept as breeding stock to try and recreate the uncorrupted black dragonflight, even if he wouldn't have been treated as a prisoner.
In Danganronpa, the school itself ultimately became this to Naegi, Togami, Aoi, Hagakure and Touko (atleast until she died) in Chapter 5's Bad Ending. All of them say they're living happily, but their huge talents have gone to waste and now they're confined to the school grounds, having a sort-of little family (and apparently Aoi is the only one giving birth to the kids, since Touko is dead and we don't know when she kicked it) that won't leave the place ever...
Elizabeth's home on Monument Island in Bioshock Infinite is an almost perfect example, consisting of a suite of lavishly furnished rooms and a large library housed within the statue of the archangel Columbia, from which she is unable to escape by any means. However, Elizabeth is completely unaware that there's a huge scientific facility built around her chambers, and a team of amoral researchers keeps her under almost constant surveillance via a series of one-way mirrors. On top of that, the tower is protected by the Songbird, a gigantic cybernetic beast programmed to terminate any unauthorized personnel with extreme prejudice.
Similarly, Eleanor Lamb from Bioshock 2 has wound up like this twice - as a child, she was taught well, but was kept under lock and key from the rest of Rapture's society via security locks, though she managed to figure out how to hack the systems. When the player finds her as an adult, she's kept in a plush sealed environment, guarded by psychotic psuedo-zombies lead by her mother.
In Cursery: The Crooked Man, this becomes an important plot point. Cheryl was feeling smothered and trapped in the chateau by her fiance, who had been obsessively keeping her from visiting her village that she escaped from their chateau one night. He was chasing her down to bring her back to the chateau when she stepped on loose ground and fell off a cliff to her death. This drove Blaise insane with grief.
In Umineko no Naku Koro ni, the Kuwadorian mansion where 1967 Beatrice stayed fits this trope perfectly. Arguably, the meta-world itself also qualifies for Battler - the surroundings are implied to be quite nice.
One of the meanings of the title The Royal Trap is how the nobility are all imprisoned by their roles and the expectations of others. More specifically, in Princess Cassidy's case, she's pretty much locked into her rooms in the castle to keep her safe.
In Girl Genius, Baron Wulfenbach takes the children of the nobles in his empire to his floating dirigible fortress as his students/hostages. They receive the best education and upbringing the Baron can provide for them, and most of the students do enjoy their life there and form friendships with the others. None of them ever forgets that they are the Baron's prisoners and hostages meant to keep their families in line.
In one mini-arc of Jack, a Fallen Angel tricks a hapless dupe into signing a contract that traps him in one of these. The "apartment" is fully stocked with material comforts (videogames, free pizza, maids w/ benefits, etc.) and he never has to work a day in his life. In truth it's a Lotus-Eater Machine in Hell that feeds off him and provides power to the Sin Vanity. When he realizes the truth, his mind is no longer able to accept the illusion and he is trapped in an empty room with no way out, his body long since atrophied.
In Our Little Adventure, Julie's former boss has been kidnapped by Brian to make drinks for him and Angelo. Judging by how well Angelo tips and the nature of the Souballo Empire, Mr. Patterson is probably living in a Gilded Cage now.
In Drowtales, the Sullisin'rune dome is lavish, luxurious, always has a party going but is unquestionably this. The Sullisin'rune are the remnants of a once great Elven empire who fled underground following a war that devastated the surface, and while they lived in peace with their neighbors the Sharen the two eventually came to blows and the Sullisin'rune lost, leaving those who remained to live in their dome under the "protection" of the Sharen. Their Illhar'ess, Ash'waren, is well aware that their dome is really a cage and that her people have grown complacent and lazy over the centuries, and she has been taking advantage of Loophole Abuse to get back at the Sharen through the Sarghress clan without technically breaking the terms of their surrender.
In morphE the Seedlings are confined to Amical's manor. It's a beautiful mansion coated head to toe with portraits, but it is still a prison that the main characters may not leave.
This is how Toph grew up. She lived in luxury and had the run of the whole estate. But she wasn't allowed to travel outside the estate or exercise her incredible potential at Earthbending — her parents thought this was too dangerous for their "helplesslittleblindgirl." Nobody other than her family and her Earthbending teacher knew that she even existed.
The Gaang's experience in Ba Sing Se. They were allowed to indulge in all the luxury they wanted, as long as they didn't try to leave, or break the rules, or evade the constant surveillance, or search for Appa, or tell anyone about Long Feng's Government Conspiracy or the war with the Fire Nation...
In the Sequel Series, The Legend of Korra, similar to Toph, the titular character lives in a large mansion with nothing to worry about except mastering all four elements in safety. However, said mansion is located in a compound miles away from the rest of the Southern Water Tribe — including Korra's own parents. It is fenced off and guarded and Korra isn't allowed to leave for even a brief period of time without permission. With an upbringing like hers it's little wonder she has trouble relating to other people.
The Venture Bros. - the Monarch, with captives Brock and Hank, think he's providing this:
Monarch: I treat my captives as kings. You shall be given the grandest of accommodations! It will be a far cry from sleeping over Dr. Venture's garage like so much Fonzie!
Hank: Hey, last time I was here you kept me in a stinky ol' jail cell!
Monarch: ...you broke my heart, Hank.
In an episode of SpongeBob SquarePants, Plankton wins Spongebob's contract in a poker game and imprisons him in the Chum Bucket until he starts making Krabby Patties. To entice Spongebob to be more co-operative, Plankton starts catering to his every whim. This soon backfires when Spongebob turns into a spoiled brat to the point where Plankton begs Mr. Krabs to take him off his hands.
The largest bases in Iraq created hotel-style "Freedom Rest" facilities where Coalition soldiers could take time off. While inside the facility, soldiers were permitted to dress in civilian attire, read books, play video games, whatever they wanted. The problem was that, for safety and accountability purposes, you were not allowed to leave.note You are now reading the rest of this entry with "Hotel California" playing in the background. Have a nice day. As a result, many soldiers preferred to take time off in their tent rather than go through the bother of being caged in a hotel.
Even better, the name was likely not tongue-in-cheek at all.
There was a comfortable resort or something in Scotland during WWII where some people who knew too much were kept comfortably, but not allowed to leave. Also, some spy-defectors were also confined to mansions (at least in the UK, maybe the US as well) while the genuine-ness of their defection was being determined.
This was also done to high-ranking German officers who'd been captured. After their initial interrogation they'd be kept with fellow officers in a mansion with waiters and other amenities, unaware that this was simply to get their guard down as all their conversations were being taped.
Field Marshal Paulus of the Wehrmacht was put into one of these when he surrendered to the Soviet Union. The other German POWs? Not so much.
Legend says that Pablo Escobar's cell was exactly like this.
Sun King Louis XIV of France's Versailles was like this, as a very comfortable prison for a few months of the year for all the nobles, including plays specifically written for them by Moliere and Goldoni, more than 1,400 fountains, and more.
The living spaces were infamously small for the grand majority of them, however, and the quality of the lavatories was abhorrent. Most of the fancy courtiers lived in rooms that made the modern student boxes seem huge, and shared the lousy toilets with dozens of their fellows.
The Doge ("Duke" in the Venetian dialect) of Venice was rarely allowed to leave the lavish Palazzo Ducale. The nobles were keen on maintaining executive power and preventing the establishment of a hereditary monarchy (something which was repeatedly attempted in the 8th century). The real power resided with the Council of Ten, a body which was technically reserved for times of crisis, but in the end were the biggest decision-makers in the entire republic from the 13th century up to the destruction of the republic at the hands of Napoleon.
Despite its sinister reputation, the pre-Revolutionary Bastille was mostly fitting for this trope. It mostly housed political prisoners, and mentally ill nobles, and it was perfectly possible for a prisoner from the Bastille to get out and rise to a prestigious position in the court again, so the wardens knew well enough not to antagonize any of them. The prisoners received an allowance, as well as anything their families donated them, and could use the money to buy anything they wanted from shops within the fortress that had as good selections as in Paris outside.
Minimum security prisons are sort of like being on house arrest at a resort, except you're required to do community service and the like. Granted, the people who go here tend to be white collar offenders.
Galileo's sentence of life imprisonment by the Catholic Church was served in a nice house where he was catered to with whatever he wanted. He was even still allowed to continue with his work.
In the minds of Western Orientalists Ottoman harems were this, not so much in real life. Life in a Turkish harem tended to be monastic in nature, and only a few residents were actually expected to have sexual encounters with the Sultan, while others lived in perfect chastity. The few high-ranking members of the harem, who usually included the Sultan's mother and her handmaidens, did live a life of luxury, but they were hardly confined in the way Orientalists imagined, either — a great many Sultans found themselves ruling under their mother's strict thumb.
This is the guiding philosophy of Norway's prison system — treat inmates well, with a plush environment, in order to rehabilitate them and reduce recidivism rates.
In the Soviet Gulag, there were special prisons known as sharashki, where inmates, usually those with some talent useful to the state like scientists or engineers, were given comfortable accommodations and high-quality food, allowed to wear their own clothing, and given a good deal of autonomy in return for working on science projects like the early space program (Sergei "The Chief Designer" Korolev began his career in one).
After Napoleon's first defeat, he was exiled in the island of Elba, where he was given sovereignty over the island and had his own personal guard of six hundred men. The island was guarded by the British Navy, but that didn't stop him from escaping.
Elizabeth Bathory was sentenced to a lifetime of house arrest for the many heinous crimes she commited against the peasants of her country and the surrounding countries, only being allowed company long enough to have food and drink delivered. Even though the bit about her bathing in blood is probably myth, it's certain she was vain, so leaving her alive to grow old and ugly without allowing anyone to see her while she was still youthful may have been A Fate Worse Than Death.
Truth in Television, the practice of exchanging hostages throughout history generally involves treating them very comfortably, though they were still prisoners that their captors could execute at any time should the other party break the deals with them.
Similar to the Bastille example, the Tower of London was used as a prison at various points in its history, but it was originally built and used as a royal residence and fortress, and when it was used for prisoners, it was almost always for nobles or other high-ranking persons. As such, the accommodations were generally typical of what a nobleman could expect outside the tower, and a prisoner could buy various luxuries. Of course, some prisoners were subject to torture while there, so it wasn't that gilded.