Over the edge of the purple down, Where the single lamplight gleams, Know ye the road to the Merciful Town That is hard by the Sea of Dreams — Where the poor may lay their wrongs away, And the sick may forget to weep?
In Paprika, scientists invent a portable device that allows people to enter other people's dreams and record them. Things start going wrong when someone hijacks an insane person's dream for terrorist purposes, and then Dream Land and reality start to merge.
In CLAMP's X1999, all dreams are connected and there are a few specially-gifted individuals (called yumemi, or "dreamseers") who can travel among them and use the Dreamscape to view the future.
CLAMP's more recent works XXX Holic and Tsubasa Reservoir Chronicle depict yumemi with similar powers, but take it a step further and make the Dreamscape into a dimension of its own, which souls alone can enter and dreamseers can manipulate.
In Rozen Maiden everyone and their doll has a personal Mental World for dreams, but on the outside all these are connected through the World Tree, forming one large navigable space.
The titular heroine and most of the antagonists of Yumekui Merry are Dream Demons, all of whom come from here. Usually, the only way to get through from their reality into ours is to possess a human being as a vessel; Merry came all the way through by herself, completely by accident, and can't figure out how to get back.
Additionally, our other protagonist Yumeji possesses the ability to see the auras of people haunted by Dream Demons, and enter their dreamworlds while they're awake. He refers to the intervening space between dreams and reality as a "daydream", the concept of which puzzles Merry.
The ending of Eureka Seven movie. The final scene either takes place in Renton's dream, or the real world merged and connected with Renton's dream.
The Dreaming in DC's Sandman. This place has a huge red-light district, but most stories don't go there. There are also individual characters who are nightmares (the Corinthian, Brute, Glob), or wet dreams (Quivering Mary) or even lovely dream places (Fiddler's Green)
Another Vertigo title, the Area in Milligan's Shade, the Changing Man was originally called 'The Area of Madness', but as more entities started coming out of it, the definition was expanded to the land of dreams, the land of the dead, the place where all human consciousness gravitates.
The magic system in Bone is based around tapping into the world of Dream Land, which in this case is a "Force"-like alternate world that permeates everything and everyone.
The setting of The Maxx shifts back and forth between the "real" world and The Outback, a subconscious world resembling a prehistoric Australia populated by fantastic creatures and psychological symbolism. The Outback featured in most of the series is that of protagonist Julie Winters, but everybody supposedly has an Outback, and physical travel between them and the "real" world can be achieved by those with the proper knowhow.
The Marvel Universe has not one but several Dream Lands. Arguably the most prominent is the Dream Dimension ruled by the Doctor Strange enemy Nightmare, who lives up to his name by inflicting terrorizing nightmares on humans. Lesser known parts of the mental plane include the Realm of Madness, which Spider-Man's enemy Venom was briefly trapped on, and the Mindscape, a dimension that connects the minds of all sentient beings, the home of the 1990s superhero Sleepwalker.
Little Ego is an adult-oriented, erotic parody of the classic Little Nemo comics by Vittorio Giardino. The main character, called Ego, is a woman seemingly in her middle twenties. As in Little Nemo, each story is about her having a dream, and she wakes up in the last panel. Whereas Little Nemo talked to his mother after waking up, Little Ego thinks what she will tell her psychoanalyst.
Mother's Oats, a psychedelic underground comic, featured crackpot inventor Cecil Quill devising a means for himself and his assistant to visit the dream world. At one point, Quill pokes his head through a portal and is temporarily driven mad, having witnessed a parakeet dream.
In Aeon Natum Engel, the dreamland is devoured like in the source material Cthulhu Tech, but since its still getting digested, the mages of the Special Services, which doesn't exist, certainly didn't perform a special ritual to summon Moloch using special properties of the dreamlands, and most certainly were not killed in process.
The Land of Oz, as portrayed in the movie The Wizard of Oz, may be the best-known example of a Dream Land in modern culture. In the movie, Oz is a head-injury-induced hallucination on the part of the heroine, Dorothy. Note that the L. Frank Baum novel on which the movie is based represents Oz as a real country.
The animated film Twice Upon a Time involves a conflict between Frivoli, the land of good dreams, and the Murkworks, the land of bad dreams.
In the film Dreamscape, agents for good and evil enter the dream world of the President—the latter to assassinate him from the inside, and the former to save him.
The film Inception is based upon the idea of creating a dream land inside another person's brain and entering it mentally. As such most of the story's events take place there, or even all of them.
The A Nightmare On Elm Street series, particularly the later films, where the children discover they can use hypnosis to enter the dream world together and give themselves superpowers.
Dreamland has the protagonists living between Real Life and such a world. Most dreamers are unconscious but those who overcame their phobia during a nightmare become Travellers, are granted a specific power, and can wander freely in Dreamland when they are asleep.
Jodi Lynn Nye's Dreamland mixes a fantasy realm which is subject to the rules of constant change.
H. P. Lovecraft did a number of stories set in a fairly surreal and oddly-light-on-the-horror-he's-known-for Dreamlands. "The Dream Quest of Unknown Kadath" includes Nyarlathotep, an enigmatic and dangerous being found in his other work, one of the major links between this Dream Cycle and the Cthulhu Mythos.
These stories were based on Lord Dunsany's dream-like storytelling. Lord Dunsany himself also wrote several stories about the world of dreams, most notably 'Idle Days on the Yann' and its sequels.
Fantastica of The Neverending Story is made up of humanity's stories, dreams and creativity — and often takes on a surreal, dreamlike nature.
The End of the World in Ender's Game first appears as the last of several Videogame Settings in the Free Play game, but turns out to have a much more personal meaning for Ender.
In Eric Nylund's novel Pawn's Dream, for a group of magic users the dream world is very real (If you die there you can't sleep here, so you'll die pretty quickly of exhaustion), and even weirder; the "real" world is just the dream world's dream world.
Tel'aranh'rhiod (translated "World of Dreams" from Fictionary), from The Wheel of Time, is a shared dream of everyone from every possible world that mirrors real-world locations. Ordinary people sometimes dream themselves into it, dangerously, as Your Mind Makes It Real. In addition, if a Dream Walker doesn't watch her thoughts, and they stray onto sexual topics, odd things can happen, including their clothes shifting suitably.
L. Sprague de Camp's Solomon's Stone takes place in a world populated by figures from daydreams.
Clive Barker's Books of the Art contain Quiddity which is essentially this, though, in the second book, the question is asked if whether Quddity is our Dream World or if we are its.
In P.C. Hodgell's Chronicles of the Kencyrath books, the dreams of the Kencyr form a dreamscape made of their individual dreams, from which one can journey to the soulscape (the land of the collective soul images of the Kencyr).
After Hamelin was a retelling of The Pied Piper in which a deaf girl is the only one left when the Piper takes away the town's children and sends them to dream land—so she has to fall asleep to find them and bring them back.
A lot of Charles de Lint's work, relying as it does on pseudo-Jungian theory being the laws of the universe (which is actually pretty cool) does a lot with this. Most prominently with the character Sophie, who breaks electronics by trying to use them and visits/populates a whole perfectly real dream world in her sleep, although she's in her mid-twenties before she starts to acknowledge the realness. Eventually her boyfriend comes out of dreamland and lives with her. This is considerable dedication, since the relationship started when he came and gave her reward sex for saving him in the form of a crow, and she blamed his existence on a severe need to get laid when she woke up. It's all because her mother was the Moon.
For extra points, consider that this boyfriend, Jack Crow, who is 'really' a crow, is now coexisting in Newford with the crow-people, who are Native American spirits (sort of) who can turn into various corbae and mostly rent rooms from a big fat guy called Raven. Totally different origins, 'really' crows, same city. They need to meet in a coffee shop sometime, and possibly already have.
As implied by the title, John C. Wright's War of the Dreaming deals with this. Everness Mansion guards the gates of dreamland. If it is destroyed, humanity will shortly go insane.
In Voyage of the Dawn Treader, Lord Rhoop is rescued from an island where dreams come true - which seems great to the crew, until Rhoop clarifies that he doesn't mean daydreams. There is a moment where everyone recalls the worst nightmare they ever had, and shortly thereafter they turn around the ship and tear out of there as fast as they can.
An Elegy For The Still Living: Begins halfway through the first chapter and stays until the end. Environments change in ways tied only the logic of emotions. Characters appear out of nowhere. Buildings talk, giraffes dance and no one bats an eye.
Michael Marshal Smith's Only Forward uses Jeamland [sic] as a major plot point/setting. The protagonist is a private eye, specialising in clients whose psyches are being poisoned by the denizens of Jeamland.
Catherine Webb's Mirror duet is primarily set in the world of dreams where people from Earth appear when they sleep, seeking their ultimate dream. Each kingdom in this world caters to different dreamer tastes. The main character controls a kingdom which specialises in storms.
The Fraggles of Fraggle Rock can join each other's dreams by placing their heads in contact and reciting the phrase "dream a dream with me, dream a dream and see" when going to sleep. Although normally just a form of benign dream sharing; it is possible to become trapped in another character's Dream Land.
Lexx had the Dream Zone, "the time and space from where our consciousness derives." Certain aliens (and at least one human culture) could send their souls there after death, allowing them to visit the living in their dreams.
Monty Python's Flying Circus subverts this by having a man facing a firing squad being awoken in his bed by his mother. Upon exclaiming "It was only a dream!" his mother tells him that, no, this is the dream, and he really is back in front of the firing squad.
The 1998 mini-series Oktober is about a powerful pharmaceutical company marketing a drug which has the side-effect of linking people in the 'mass unconsciousness'.
Little Nemo is a renowned newspaper strip (and lesser-known film) about a boy's adventures in Dream Land.
Table Top Games
The Eberron setting of Dungeons & Dragons has this in the form of Dal Quor, filled with nightmarish psionic creatures called quori. Peoples' minds go there when they dream, and the Dreaming Dark are quori that learned to do this in reverse. The kalashtar are the descendants of humans who merged with rebel quori long ago to escape the Dreaming Dark.
Oh, and it used to be possible to get there physically, but an ancient race of giants managed to force the dimensions apart with magic. In the aftermath, they descended into savagery.
The Wall of Color between Deep and Border Ethereal is also Veil of Sleep. Walking into the thing that resembles an infinite soap bubble wall instead of through it is the only way to visit bodily a dreamscape of whatever world's border is beyond this part of curtain. Not that it's easy, of course.
Ravenloft has The Nightmare Lands where normal place is mixed with dream stuff so that even the terrain is malleable and masters of nightmares keep little dreamscape cells for the victims they drive nuts with private nightly horror shows.
The Immaterium of Warhammer 40000, a universe of the hate, fear and bad dreams of all sentient beings. Daemons and stuff too.
Mage The Awakening contains the Astral Realms, which have three distinct levels. The Oneiros is each individual's personal Mental World. The Tenemos is the Dream World of humanity, containing the sum total of all human knowledge, belief, and experience, albeit shrouded in metaphor, symbolism and subjectivity. Each concept has its own realm, and they are either ruled over by gods (all gods ever beleived in exist in the Tenemos) or archetypes. Travel is made by locating aspects in one realm and moveing to another connected to it by word association. It is possible for the realms of ideologies to enforce belief in their ideology upon visitors. Even deeper is the Anima Mundi (also called the Dreamtime), which is essentially the Dream World of the Earth itself. Its entirely inhuman perspective can wash away any unprotected human mind that tries to pass through it. It contains the Earth's perspective on humanity (represented as a vast swath of destruction), nature (which is filled with animal and elemental archetypes; notably, the animal archetypes are devoid of Animal Motifs) and the wider universe (represented as an incomprehensibly large void filled with bizarre objects and beings). All Astral Realms operate on subjective time. The length of real time one spends in the Astral Realms largely depends on the degree to which you interact with them (so, for example, if you merely pass through a desert, it might feel like hours, but in real time, it will take about as long as it takes to say "I pass through the desert").
Changeling The Lost has its own dream network, known as the Skein. Word Of God says both the Oneiros and the Skein are the same thing, but the differing structure relies on the mindsets of the supernatural types. To the mages, the dreamscape appears an endless tapestry of human thought, whereas to the changelings, it appears a labyrinthine structure of ornate chambers decorated with the dream stuff of a billion sleepers.
Arkham Horror, being Cthulhu MythosThe Board Game, features the Dreamlands mentioned above as an Other World location to be explored. Like it's source material it's a surprisingly "gentle" location compared to, say the Plateau of Leng.
The small-press RPG Shattered Dreams is all about Dream Land adventures and battling its monsters that prey on dreamers.
Franco Dragone's Las Vegas spectacle Le Reve ("The Dream") takes place in a woman's dream. There's plenty of sexuality and surrealism to go around. Dragone used to work for Cirque du Soleil, and his last show for them, La Nouba, is set in an attic where humanity's fairy tale dreams and nightmares coexist. (In part because it was commissioned for Walt Disney World, it's not nearly as suggestive as the latter show.)
Dream Land of the Kirby series is a variation. It is home of the Star Rod, which powers a fountain that makes the residents dream. A nightmare once tried to enter the world through the fountain so the Star Rod was removed to keep him away, at the price of no one being able to dream.
Yume Nikki (lit. Dream Journal) is based on a Hikiko Mori girl who spends all her time sleeping then recording her dreams. The game features a vast, sprawling world of surreal dreamscapes, full of very interesting sights. The only real objective is to collect "Effects," which let you do things in your dreams like change your hair, ride a bike, or transform into weird objects. Get it here.Then hide under the bed. This girl has issues.
The DreamWeb from the eponymous video game is an interesting example, as it subconsciously influences humans in their sleep and thus shapes the future of mankind. Then, someone tries to pervert it for evil purposes...
As it turns out, in Final Fantasy X, Zanarkand is merely the "dream of the fayth" - when they awaken, it disappears.
Supposedly, LittleBigPlanet is made from the creative energies of people that are dreaming.
In Tsukihime, Kagetsu Tohya. The story is only focused around Shiki and only appears to encompass the town he lives in, plus the next one over. However, it's revealed that actually, all the people he meets are indeed 'real' in a sense. They can give him information he needs to figure out what's going on and will also realize the oddness of the repeating days in their own ways. The dream he's in also mixes all the different Tsukihime continuities heavily, though Shiki does not notice.
Keen Dreams, episode 3.5 of the Commander Keen series, takes places entirely inside a dream world.
The entirety of Dare To Dream takes place in the mind of the player's character.
Dragon Age: Origins has this covered in the form of the Fade, the place where the spirits of every species except dwarves go when asleep. It's very...odd. Mages are the only people who can consciously navigate it without having to check on wether they're dreaming or not, though this puts them in danger of being possessed by the many demons that wander the Fade.
The mental worlds in Psychonauts are a bit like this, since a few kids mention that they've been having dreams about things that appear in peoples' heads.
Legend Of Mana - The entire world of Fa'Diel is believed to be a Dream Land by the Storyteller and the Sproutlings, but the universe itself also has a dream world that the player character can visit on several occasions.
Final Fantasy VI's dream sequence in which Cyan puts his family's death behind him.
Sector 4 in Jumper Two takes place in Ogmo's nightmaredream, which he fell into while falling.
Pokemon Black And White has an added online game feature called the "Dream World", in which asleep Pokémon explore their dreams. It is similar in gameplay to the Pokéwalker, but without the added benefit of getting kids to go play outside.
In Rayman Origins the entire world was created by the Bubble Dreamer, a godlike entity that does nothing but sleep. His nightmares are what cause dangerous things to happen.
You go through a number of these in Kingdom Hearts 3D [Dream Drop Distance]. On something of a different note, they're made from the dreams of worlds that have yet to fully awaken following their restoration at the end of the first game. This allows the game to show events in the series' past (King Mickey's adventures as both Yen Sid's apprentice and a musketeer) and revisit the Pinocchio storyline. Sora is confused when Jiminy Cricket doesn't recognize him, then remembers this is that world's dream of Jiminy.
Of course, prior to the Hob storyline, most of the comic had this feel to it, even if it wasn't technically taking place in a dream or a comparable plane of existence.
YU+ME: dream has elements of this, if the name didn't tip you off. Fiona starts out as someone who hates life so much that she dreams constantly, though these turn out to be a version of Dream Within a Dream. We come back to Dream Land concepts as Fiona wakes up from her coma and subsequently goes back to find Lia.
In End of Infinity, Phantasmagoria is the world that dreamers go to when they're asleep. By taking off their Placidus mask, they can become Lucid Dreamers and interact directly with the Phantasmagorians, permanent residents of the dream world. Otherwise, they are Placid Dreamers, who experience Phantasmagoria as an ordinary dream.
Homestuck initially seems to do this, with Jade dreaming that she lives in a beautiful tower on a golden moon. It doesn't take long until it's established that said dream lands, Prospit and Derse, are just another part of the physical plane in which Sburb takes place, primarily accessed in the players' sleep through their dream selves.
Foster's Home for Imaginary Friends has its own version of this trope; in the special, Destination Imagination, the characters go on an adventure through an entire imaginary world created by a kid and controlled by the childish imaginary friend inside.
Imaginationland from the South Park episode of the same name.
The cartoon Somewhere in Dreamland is pretty much what you'd expect.
In Adventures in Care-a-Lot, all the Care Bears' dreams occur in one connected dreamland that looks just like Care-a-Lot. Accordingly, they tend to dream about doing the same things they do when they're awake.
In an episode of Gargoyles, Goliath and former Pack member Dingo are put into a trance and sent into the "Dreamtime", in order to stop the Matrix from covering the world. In this world, they have control, allowing them to create weapons out of thin air.
The episode "King Worm" of Adventure Time uses this trope to its trippy potential.
The Superjail! episode "Dream Machine" is even trippier than AdventureTime's "King Worm". But then again, it IS Superjail...