Marsupials and some other animals have pouches to carry their young. This trope covers fictional creatures with a built-in cage or cavity in which to hold a prisoner captive, or possibly a group of captives, usually the Damsel in Distress, the sage, the hero's Love Interest, or another loved one. The prisoner often has a view to the outside world, the better to cry for help. They may also be unconscious, or partially merged into the creature's flesh.
This is often a cage (or ribcage) with bars made of bone and flesh, or sometimes an extra mouth full of sharp teeth. A Blob Monster is often involved in cases where the prisoner is merged with its captor. May involve being Swallowed Whole, in which case Getting Eaten Is Harmless. It can also be a Crystal Prison or a bubble of translucent flesh. In about half of all of the latter two cases, you can often expect the prison to also be the enemy's power source and weak point. Most of the time, however, the monster will use its captive as a Human Shield instead forcing rescuers to be careful in their attacks.
Invariably a case of Our Monsters Are Weird, this monster is often a Giant Mook in service to the villain, but may be the Final Boss, and possibly even the villain themselves after they go all One-Winged Angel. Often a demon, Giant Space Flea from Nowhere, or giant skeleton. On a less monstrous note, it may be a robot Super Cop with one or more containment pods, or a whimsical animal with Bizarre Alien Biology. Heroic examples tend to be rare, but can happen, typically by playing up the cartoonishness of it.
This is not the same as a Womb Level: the character may or may not be in danger of being digested or having their soul devoured, but they're stuck inside the beast, not walking around inside its guts.
- The COVERS of Kill la Kill pull people inside them trapping them leaving only a small face visible.
- The sludge villain of My Hero Academia has trapped both Midoriya and Bakugo before attempting to enter and take control of their bodies, even using Bakugo as a Human Shield when confronted by heroes.
- The infamous One Piece movie Baron Omatsuri and the Secret Island has the Eldritch Abomination Lily Carnation with the Straw Hat crew stuck inside it and being digested.
- Pokemon Jirachi Wish Maker has the monstrous Groudon that Butler ends up creating, which sucks up Pokémon and humans with slime tendrils and traps them inside bubbles in its body.
- Smile Pretty Cure! Majorina conjours up an apple-shaped Akombe with a cage that it uses to trap Naos siblings.
- The Gourmet Corp. use a strange skeleton beast with cages on its shoulders to capture chefs during the cooking festival.
- The IGO also uses beasts that grow cage like structures on their backs to transport prisoners to the honey prison.
- One of Benares Juuma from 3×3 Eyes is an insect-like creature with a voluminous bubble-shaped abdomen, which can be used to inglobate and seal enemies.
- Seaman from YuYu Hakusho can create water monsters, which can imprison people within them. Later on, Itsuki can summon a bidimensional demon which can swallow others and keep them sealed inside a separate dimension.
- Hellblazer: In "All His Engines", a demon has stolen Chas's granddaughter and keeps her in a cage inside him. He allows John inside to see her, but John ends up covered in gunk as he lunges for the cage, so it's not surprising that she interpreted John's "We're coming to get you!" in an entirely different context.
- Green Lantern introduces the ghoulish hag Kryb, member of the Sinestro Corps, whose favored method of instilling fear is to murder Green Lantern couples and kidnap their now orphaned newborns. She keeps the babies in a cage-like pouch on her back, and is able to secrete a mind-controlling liquid which she feeds them.
- In the My Little Pony: Friendship Is Magic fanfic Sharing the Night, dragons are immortal beings who never stop growing, eventually becoming titanic things of living earth and rock, entering nearly eternal hibernations and becoming part of the landscape; almost every part of Equestria is made up of unimaginably ancient dragons sleeping on top of and around each other. Tartarus, specifically, used to be a dragon by that name who decided to contain all evil beings in the world by swallowing them and imprisoning them within himself. By the time he entered his permanent, rocky hibernation, he had become a living, cavernous prison still holding an uncountable number of ancient horrors imprisoned in his gut, which had been transformed and partially "digested" to become a host of lesser monsters that still wriggle to freedom past his jaws every now and again.
- Disney's Alice in Wonderland. While in the Tulgey Wood, Alice meets a "birdcage bird": a large bird with a birdcage as its trunk, a head and two legs. It has two small birds inside its body. When Alice bumps into it, the door on the birdcage opens and the two small birds escape. The birdcage bird runs after them and swallows them, returning them to the inside of the cage.
- Animorphs: Erek, an android, reveals that the Chee are doing what they can to fight the Yeerks, sluglike parasites that wrap themselves around the host's brain and control them, but need to leave the host every three days. By pretending to be infested, they trap Yeerks inside their own cranium and extract information from them.
- In Myth-ing Persons, Aahz is imprisoned in a living tower with the head of a gargoyle. Designed to hold vampires, it swallows any who try to escape in corporeal form, and inhales any who try to escape in mist form.
- Kamen Rider OOO: While most Yummies grow by acting out the desires of the human they were spawned from, the variety created by Kazari are instead parasites that influence that human's behavior. When they reach their adult form the host becomes trapped inside their body, forcing OOO to find some way to get the human out before he can destroy them.
- Doctor Who S2E10 "Love and Monsters": The baddy of the week is a Fat Bastard alien expy who absorbs his victims, where they become part of his body. Near the end, we see his victims' faces jutting out of his skin. They actually cooperate and push themselves outwards, which eventually weakens the monster enough to kill it.
- Dungeons & Dragons: An odd case with the devourer from the Monstrous Compendium III for the Planescape setting — a towering, cadaverous undead monster with a shriveled, doll-like figure trapped inside of its ribcage — the soul of one of its victims. While the victim is dead their soul can still be rescued. It continues to seek out new mortal victims to prey on, as each trapped soul's life force is drained.
- Many larger Transformers figures had storage for smaller figures, some of which were identified as jail cells or prisons due to Rule of Cool:
- The original Fortress Maximus figure had a jail cell concealed in its left leg. Given Fortress Maximus was a Cityformer, that makes sense. This likely inspired his characterization in the IDW comics as warden of a prison.
- Transformers Armada Megatron has storage for Mini-Cons. What makes it likely to be a prison is the fact that Megatron also has a capture claw for Minicons.
- From the same line, Unicron is filled with Minicon storage gimmicks. The animation makes it clear that the Minicons are not in there by choice.
- The Titans Return Trypticon toy featured the gimmick of being able to swallow Titan Master sized figures while in dinosaur mode, who are then trapped in his chest. As he's another Cityformer, he's shown in some comics and animated series to actually have cells for holding normal sized Transformers.
- In Arc the Lad obtaining Gogen requires fighting the Illusion Lord. The monster is a large blue genie-like creature holding Gogen trapped between its hands and using his magics on your party during the fight.
- Bayonetta 2 has the monster Alraune, whose hollow chest cavity in her One-Winged Angel form contains Jeanne's lost soul.
- In Breath of Fire II there is a boss with a figure listed as old man chained up to the side of it, killing the boss without killing the man allows you to rescue them.
- Chrono Cross: Schala turns up during the final battle inside a crystal, which is actually the backside of the Time Devourer. Freeing Schala without killing her is how you unlock the Golden Ending.
- Dragon Quest XI has a class of monsters which appear as porcelain dolls with a birdcage where their legs would be. These monsters can trap allies inside their cages rendering them immobile until freed.
- In Final Fantasy VIII, Adel, the first boss of the story's last fourth, imprisons Rinoa on their chest at the beginning of the battle to periodically drain HP from as well use as a Human Shield. Rinoa not only takes damage from Adel's HP drain, but can be deliberately targeted, will get caught in any AOE attack you launch, and can eventually die from all that, resulting in a Nonstandard Game Over.
- The first major boss battle in Final Fantasy IX is against a giant plant monster currently holding Garnet trapped inside the cage formed by its own body. The battle is a Forced Tutorial that introduces the Trance mechanic to the game.
- One of the boss battles in Girls And Dungeon involves a mimic who captures one of your companions in its mouth, forcing you to use only single-target attacks for fear of hurting the companion.
- The Parasite Cage Heartless in Kingdom Hearts I is, aptly named, a large monster that spent one of the two battles with it keeping Pinocchio trapped behind its bar-like teeth.
- In Kingdom Hearts II, Maleficent summons a Heartless called "Prison Keeper" which has a cage as part of its body, and it holds Lock, Shock, and Barrel in it until it has need of their abilities, in which case it swallows them.
- In Legend of Dragoon, the Final Boss's second form can suck up a party member and keep them prisoner for a while inside it, before firing them back out to damage both them and whoever they were launched at.
- Mario & Luigi: Bowser's Inside Story: Among the enemies encountered in Bowser's castle after Fawful takes it over are the Jailgoons, which resemble large living cages with feet and with a cannon and shield for arms. Each Jailgoon contains either a Goomba or a Bob-omb, minions that evidently remained loyal to Bowser and that Fawful thus locked away inside the Jailgoons.
- In each world of Rayman Origins, one of the five Bodacious Nymphs has been captured inside of a Darktoon, with the latter's teeth acting as jail bars. Rayman and friends then have to chase the Darktoon throughout the level and defeat it in order to free the Nymph and unlock a new ability that will aid them throughout the rest of the world.
- Rayman Legends sees the return of the Tricky Treasure levels as part of the Back to Origins bonus levels that were originally part of Rayman Origins, in which Rayman has to chase living treasure chests in order to gain a Ruby Skull Tooth. In Legends, the treasure boxes contain a captive Teensy Jester instead, making it this trope.
- In Inhumanoids, the character D'Compose used his ribcage as a prison.
- This is Gagoyle's main shtick - he can gobble his victims whole straight to his stomach, which is transparent. Then bystanders can watch as they are slowly dissolved by its acid. Thankfully, Gagoyle can vomit anyone out intact, sans their dignity.
- The New Adventures of Winnie the Pooh: At the beginning of "There's No Camp Like Home", Piglet has a nightmare about being chased by heffalumps and woozles, ending with him being behind bars inside a police heffalump's stomach.
- When gems in Steven Universe fused together, they turn into amorphous light before reforming into a new body. The Topazes exploit this by forming the merged body around people to hold them captive. The abducted humans she holds inside are engulfed almost entirely◊, usually only exposing eyes, noses, and parts of a few helplessly flailing limbs.
- Wakfu: Shuhsu General Anathar has what at first glance could be considered a Belly Mouth, surrounded by crustacean-like legs, except he doesn't so much eat things with it than uses it as storage, including small creatures like Rubilax (in sword form) or Grany Smisse (in bow-meow [housecat] form).