Say you're a Space Marine in a completely normal space facility. You pass by an innocuous piece of wall, and then suddenly - SHOOM the wall opens behind you to reveal a 2-foot by 2-foot square completely empty except for a demonic space monster trying to burn the back of your head off.
Primarily a First-Person Shooter trope. It's mainly present in older first-person shooters as it's becoming largely discredited, due to better storytelling techniques or replacing it by offscreen or onscreen spawning.
One must question a few aspects of this situation:
- Why is there a random closet in the wall that isn't being used?
- Why is it hidden? (Although being hidden does sort of explain why they weren't used)
- Why do so many of them have monsters in them? How did they get in there in the first place?
- Why does it automatically open as the Player Character passes by? If the monster could open it from the inside, why did it stay in there?
A form of Malevolent Architecture.
- In The Matrix: Path of Neo there's a level where vampires start bursting out of walls and columns with no way, logical, way of getting inside said walls and columns.
- In Metroid Prime, the first Sheegoth that you fight bursts out of a wall that was concealing a room just big enough for said Sheegoth, with no way in or out.
- In La-Mulana, removing a certain section of wall in the Temple of Moonlight releases a whole bunch of Goddamned Bats. Amazingly enough, this is not a trap.
- Spider-Man: Edge of Time: The 2099 levels adore this.
- Several Final Fantasy games have the "Monster-in-a-box!", special encounters (often with a special opponent and rare loot) whom you face when you open a seemingly innocent treasure box. Why, exactly, are the monsters hiding out in the boxes?
- There are plenty of monster closets in the High Entia Tomb in Xenoblade. The "monsters" that jump you are ancient machines built to guard it. And there's a twist too, exactly one of them is more than just a closet: it's an actual secret passage that leads to a hidden area.
- Doom did it a lot. The Trope Codifier, along with Teleporting Keycard Squad. Often times rooms would be just a pedestal with an item on them, but taking the item opens up all the walls to reveal nasties. If you see a key or very good item, expect the baddies to pop out as soon as you get it.
- They did it with Doom 3, where it stretched believability to the breaking point. "They're breaking through the walls!" (radio transmission)
- Lampshaded in the Game Mod Claustrophobia: The Walls Close In, where the protagonist is dumbfounded to see apparently normal walls inexplicably opening and releasing monsters.
- Before Doom 3, the Descent series was the king of this trope. You could often find dozens of these in every single level. Descent also justifies the trope as the robots setting traps for you, and since they are, in fact, mining robots, it makes sense that they could carve small rooms out of the walls of the level for this purpose.
- The first Unreal, has one moment near the start. Up to that moment you've only encountered Brutes (slow and easy to kill, if quick to shoot), tentacles (plants that shoot nearly harmless spikes) and birds (quick but easy to dodge and kill), wiping out the whole of them. The task at hand is to deactivate a generator powering a forcefield. Upon coming back from this task, the long, narrow corridor you've already walked through before starts getting dark, as lights switch off. Right about the time you start to wonder what the hell's going on, a Skaarj Warrior jumps out from the darkness from a previously closed closet-sized empty room and proceeds to scare the living daylights out of you.
- Half Life 1 explains it by way of the monsters getting into unused drywalled-off corridors due to random teleporting. And at least one common enemy creature, the headcrab is an ambuish predator that intentionally seeks out dark corners to lurk in. Half-Life 2 played this up to near-Survival Horror levels of tension and creepiness in places.
- Hordes of 30 zombies spawning out of a closet is pretty much one of Left 4 Dead's main game mechanics. You will encounter plenty of zombie configurations that will make you stop and ask, "How the hell did this happen? How did these guys get here? Why did they stay?"
- It can also lead to unintentional hilarity when a witch spawns in a closet. Open door, toss in molotov, close door, wait for the screaming to stop. Repeat as needed.
- The Quake series does it sometimes in the first 2 installments.
- Many examples in Duke Nukem 3D, many of which could be avoided by using the jetpack to quickly fly over the Event Flag.
- In Clive Barker's Undying, this happens with a skeleton while you're around the monastery catacombs.
- Happens once in the subway level of Condemned: Criminal Origins — the player opens a locker and gets jumped by a pale, emaciated woman wielding a rebar.
- The final boss fight with Korax in Hexen is about chasing him as he teleports and opens doors to Monster Closets.
- First Encounter Assault Recon has one in Interval 7-2 where a Replica squad ambushes you from behind a revolving office partition. There are also the elevator ambushes throughout the game.
- Start shooting SHODAN's CPU nodes in System Shock and watch as an inordinate amount of cyborgs pop out of maintenance closets.
- Portal explains where the turrets-in-the-walls come from by showing you a whole distribution system for them criss-crossing the entire facility.
- These are called "vaults" in the roguelike genre, though typically they don't open up on their own; either they have (often hidden) entrances, or you have to dig your way in.
- Dead Nation: Hordes of zombies will pop out of small buildings, trucks and buses when you draw near.
- In Dead Space, the necromorphs pop out of vents, floor tiles, the ceiling; outside of a few rare circumstances you never run across them in the open. After a while you can pick out exactly what parts of the wall the Necromorphs will pop out of Dead Space and Dead Space 2 although Dead Space 2 just skips the closet outright at times and has monsters magically appear.
- All three games have vents. And 2 has several sequences where the player themselves must crawl through service tubes. You can tell where this is going.
- Skewered and fricassed in Zero Punctuation's Review of Dead Space 2, a modern adherent to the original version of the trope. The narrator notes that monsters pop out of identical air vents so often there's no surprise when they do, but that the air vent doesn't go anywhere, suggesting the poor beastie had to pry off the cover, put the cover back on once it was inside, and just take a nap. Since Dead Space is a Survival Horror game, knowing where the enemies are all but guaranteed to jump out from certainly removes a ton of suspense.
- Resident Evil: Dogs and zombies coming through windows? Check. A zombie bursting out of a literal closet? Check. Licker crashing through the one-way mirror? Check.
- Oven Man from Resident Evil 4. Leon will even lampshade this by wondering what he was doing in there.
- Dino Crisis: A raptor leaps out of an electronics zone in the wall during the Underground lab segment. It's hard to see what it was doing there.
- It's been almost entirely replaced by "Ah, they're coming out of the air vents!" in video games. For instance, Mass Effect does this with some of the rachni on Noveria. Though the exact same problems apply to those as do to the monster closets.
- Happens in Ayleid Ruins in The Elder Scrolls IV: Oblivion, though this is at least handwaved by the fact that Ayleid ruins are notorious for being booby-trapped.
- Vault 34 of Fallout: New Vegas has an interesting take on monster closets. Because the player effectively has radar, just hiding monsters in secret wall panels wouldn't do, so instead the vault features several feral ghouls (universes version of zombies) trapped in various temporarily inaccessible rooms, which convenient glass picture windows so that you very much know they are there. The power doors pop open when ever you pick up certain items or perform certain tasks required for opening the Vault's armory. However normally the opened door will be on the other side of the vault, so the ghouls often spread out when they are released and you can seldom be sure that you've eliminated all the free ghouls.
- Then there are the Spore Carriers from Vault 22. They hide in pods in large clumps of fern, amid an overgrown interior, so they are easy to miss, and they do not show up on your radar untill awakenening, usually behind your back...
- Parodied in Undertale. You first encounter Mettaton after he bursts through a wall in Alphys's lab. After the encounter, you can inspect the hole he came out of to discover there's only just enough space behind the wall to fit him, which means he was deliberately waiting in the space between the walls just to jump out at you.