Follow TV Tropes


Lock and Key Puzzle

Go To

One of the two fundamental Adventure Game puzzle types. This sort of puzzle is based on collecting an item or items from somewhere in the model world, and delivering them to some other place, where they can be of use.

The archetype of this puzzle design is an actual physical lock. The player must retrieve the corresponding key from somewhere else in the world, and bring it to the door. Another very common form is a non-player character who performs a task which alters the state of the game world when he is given the proper payment. Another variant uses a combination lock or similar that requires a code, and the player has to determine the right answer from hints in in-game documents.

In its simplest form, the player must do nothing more than bring the relevant object to the right place in order to solve the puzzle. Games with a more sophisticated user interface will require that the player use the "key" in some way specific to the nature of the puzzle, though in unskilled hands, this can lead to a Guess The Verb puzzle.

The Lock and Key Puzzle is one of the oldest and most common puzzle types across adventure games, especially Interactive Fiction. Its advantages include a tighter coupling with the model world than the Set Piece Puzzle. The setup is also easy to couple with plot developments, using the "key" as a Plot Coupon. The major disadvantages of this puzzle type are, on one hand, the possibility of Combinatorial Explosion and, on the other hand, the possibility of This Looks Like a Job for Aquaman.

See also Broken Bridge. If the "key" is something non-intuitive or ridiculous, you've got to Solve the Soup Cans. For examples that are literal locked doors that require a key, see the subtrope, Locked Door.

Video Game Examples

  • This one dates back to the dawn of Adventure: the goal of Colossal Cave is to deliver the various treasures in the game to a treasure room.
  • Chip's Challenge makes use of color-coded keys and doors in many ways for this purpose, with the player being required to collect a certain number of chips each level to get through the gate to the exit. Two examples in particular stand out:
    • Level 135 (Trust Me) requires Chip to find one yellow key to open the yellow door blocking the exit. The problem is that, while there are multiple keys, many of them are either tied to deadly traps or simply inaccessible; as a result, he has to navigate through the whole level to figure out which is the right key to collect. There's a glitch in the Microsoft version that allows an earlier key to be grabbed without consequence to finish the level more quickly, though.
    • Level 137 (Goldkey) features many yellow keys as well as many yellow doors. The catch here is that certain doors have to be opened in a particular order, as going through either a wrong path or a certain area too ahead of time will render the level Unwinnable by Design, forcing the player to restart it.
  • The ancient TinyMUD had a wonderful in-game language for constructing new puzzles. As long as they were lock-and-key puzzles. That was the only type you could build.
  • The two Detective Barbie PC games had this, although it wasn't always literal keys.
  • The NES game Castlequest was one gigantic version of this.
  • Several puzzles in the later Wizardry games ultimately boiled down to this, though quite often the nature of the item you need is only hinted at, and said item is hidden half a world away. Also common in reverse: you find the strange or seemingly useless item first, then much, much later, find the place you need that odd item.
  • In the first Mega Man Legends game, you had to find starter keys hidden in dungeons in order to drop the shield that housed the refractor. In the second to last dungeon you had to find ID cards.
  • The Stoneship Age in Myst has a literal one, besides the fireplace panel in the library with over 280 trillion possible combinations.
  • Riven has its infamous "Waffle Iron" puzzle which requires you to place up to six marbles with different colors somewhere in a 25x25 grid. The total amout of possible combinations is in the quadrillions. Knowing a few of the criteria reduces the number down to a "mere" 93,850 trillion.
  • Doom
    • The closest thing there is to a puzzle in the classic games. There are three different keys (red, blue, and yellow, all three in "keycard" and "skull key" variants, but only one variant appearing per level), each of which opens matching-color doors within the same level. Which keys appear (if any) depends on the level, and the format depend. Later on, fans cooked up source ports that allow the game to distinguish between key formats as well, so in custom WADs, a man-made electronic keycard doesn't open.
    • Doom³: Pops up in three different flavors. The most common is restricted-access doors that require a scan for your PDA clearance, and you have to find the PDA of one of the people authorized (which the door's interface panel helpfully provides a list of) to download the clearance and gain access; sometimes, you have to find an actual keycard; and finally, certain areas have to be unlocked by accessing a security terminal.
    • Doom (2016) varies things up a bit by occasionally making the "key" you have to find a severed hand from one of the mangled corpses lying around. Or an entire torso.
  • Wolfenstein 3-D and the later Quake both have gold and silver keys (also keycards and runekeys in the latter, depending on the level aesthetic). Most of the mid-90's "Doom clones" like Duke Nukem 3D, Dark Forces, and Blood also copied this idea. Blood is noteworthy in that it features six different key types (dagger, eye, fire, moon, skull and spider), though levels rarely feature all of them at once.
  • In The Elder Scrolls III: Morrowind, in the dungeons of Tel Fyr, there is an unmarked quest involving a series of locked chests. Each contains some minor loot and a key for the next chest. Get to the final chest and you can walk away with a few legendary weapons and the best Light Armor cuirass in the game.
  • There are at least two puzzle like that in Spellforce. While not mandatory, they offer nice loot. They reappeared in the sequel, as well.
  • The more plot-driven Mystery Case Files games all end with variations of this.
  • Almost all dungeon levels in the Dark Cloud series feature this. The dungeon item will invariably be dropped by one enemy on the floor upon defeat, which will be used to travel to the next floor. Occasionally, you'll find keys that will open up doors or bridges that block off parts of levels.
  • raocow refers to these as "item babysitting" in Super Mario World ROM hacks: finding a key and bringing it back to a lock you passed, finding a springboard and bringing it back to a high jump you passed, etc. He's not particularly fond of these puzzles, but it's about all the complexity and nonlinearity one can manage in the Super Mario World engine.
  • Eternal Darkness has many of these puzzles. One notable example is the "Staff of Ra"-style puzzle where the character finds a rod and a lens, puts them together and places the staff on a pedestal. The sunlight (or whatever it is) coming from above focuses through the lens into a beam, which must be rotated to reveal reflective panels before finally unlocking the door.
  • Pokémon has at least two of these. In Pokémon Red and Blue and Yellow, plus FireRed and LeafGreen, you have to find the key card for the Team Rocket hideout to get through it. In Pokémon Diamond and Pearl and Platinum, the key card is needed for the Team Galactic building.
  • Maniac Mansion is all over this. Finding all the keys (including keycodes), figuring out which lock they open, and getting things from the locked rooms comprises most of the game-solving puzzles
  • Missing Children has quite a few locks for which you need to find keys.
  • Randomly-generated Adventure Construction Set games consisted of nothing else. All but one of the dungeons would contain a locked door with an NPC demanding a specific item. The remaining dungeon would have the item that starts off the chain.
  • Very common in The Castles of Doctor Creep. While not all the exit doors to the castles are locked with keys, all the castles require the collection and use of keys to proceed further in the level.
  • One of the stranger examples appears in Doom RPG, in which the 'lock' is a large database with a piece of vital information buried in it somewhere, and the 'key' is getting an NPC to loan you a Beginner's Guide to SQL so you can look up the right command. Regrettably, the limits of the game engine prevent players who already know the command they need from bypassing this.
  • Locked doors and color-coded keys are present in the Domino Dungeon and Plizzanet levels of Yo! Noid 2: Enter the Void. The puzzle is finding the keys.
  • One of the quests in Withstand involves locating a key card that you need to open a door.
  • The Pedestrian (2020): Sometimes The Pedestrian will need to bring a key to a locked door to progress further.
  • Dead County: There will come times when the delivery guy needs to hunt down keys to unlock doors.
  • String Tyrant: The player progresses the manor, by finding keys to open doors. These are helpfully labeled with card suites both on the key and relevant door.
  • Sydney Hunter and the Curse of the Mayan contains many examples of different-coloured skull doors that require the appropriately-coloured keys to unlock.
  • Pacify: Multiple doors in the house are locked, and the keys are scattered all throughout said house.
  • Onryō (2020) has plenty of locked doors you need to find the key for.
  • Blame Him has its share of locked doors that require keys to open. Luckily for the first one, the key's in the same room.
  • HEPH begins with the Player Character in a locked room that requires a key card to get out. The only way to get it is to make one from the resources acquired by breaking down objects in the room.
  • A-Tech Cybernetic has its share. The thing is, you just need to have the key in your inventory, and you can unlock the corresponding door by placing your hand on the scanner.
  • Clea (2019): The doors to clear the levels are all locked, and you need to find the keys. Said keys are all separated into three pieces, so you need to find and combine them so they can work.
  • Castle in the Darkness has a number of doors you need to find a key for.
  • Today Is My Birthday has locked doors, and you will need to find keys for them.
  • Hanako: The school the game is set in is FULL of locked doors. Each one needs the corresponding key to open it up.
  • Ninja Outbreak: There are differently-coloured doors in the game that need their corresponding keys to unlock.
  • Lunch Lady: Plenty of doors in the school are locked, and you need to find the keys to open them.
  • Trenches (2021): There's at least one locked door in the game you need to find the key for.
  • The Caregiver: The shed at Souichi's house is locked shut, and the key's in a box with a rusted lock.
  • Roots of Insanity: One of the first puzzles faced in the game is locating the key to B block.
  • Eldervale: This game has its share of locked doors you need to find keys for, alongside ones you need to unbolt from the other side.
  • Livestream: Escape from Hotel Izanami: Plenty of rooms in the hotel are locked, and require a key to open.
  • Ecco the Dolphin: The majority of the series' puzzles are in this format. "SEARCH FOR THE KEY-GLYPH" indeed.
  • Kolibri: This shooter has both autoscrolling levels and puzzle levels. The vast majority of the puzzle levels are in this format, requiring Kolibri to find a single-use powerup to blast through stones in his way.
  • The Night Way Home: One of the first puzzles in the game is to find the key to the security room.
  • Alisa: There are plenty of locked doors in the dollhouse that Alisa needs to find the right key for. The keys she finds, she keeps on her key ring.
  • Harthorn: The school has changed and updated their locks in favour of key pads and key cards following an unspecified incident. Despite this, you can still find keys that open locked doors.
  • Sherlock Holmes: The Mystery of the Mummy: Sherlock Holmes can find a key in the mansion to a locked door. However, he refuses to use it right away on the grounds that the lock is so rusted it's liable to break the key. So you'll need to find an oil can to use on the door first.
  • KOJOUJI: There are locked doors in the game you will need to collect certain key cards to be able to open. You start the game with the missing person's key card.
  • Ninjish Guy In Low Res World: There are some parts of the game that only open up if you grab the key.
  • The Radio Station: You can't get into the titular radio station until you find the key.
  • Blood Breed: There are plenty of locked doors in the Killamoor Meat Works that the Player Character must find the key to.
  • Mario Party 7: The Bowser minigame Treasure Dome! has a solo player open five chests, one after another, and has only 30 seconds to do so. At the start of the minigame, the player grabs the key at the center and has to see which chest is opened with it, and that chest will have the key that opens one of the other four chests, then get the next key to see which of the remaining three chests opens up, and so on. The fifth chest opened guards the key that allows the player to open the exit door.
  • HAAK: In the Sanho Ruins, there are plenty of locked doors that can only be opened by blue keycards.
  • Castle on the Coast: The main objective of the game appears to be collecting the four keystones to get into the main tower. In addition to that, there's a few locked coloured doors that need their corresponding keys to open.
  • Madman (2022): There are locked doors in the hospital that will only open with the corresponding key card.
  • Many puzzles in Cragne Manor involve finding keys to open boxes or doors. Sometimes they're for items in the same room, while other ones have to be brought across the game. Your backpack has a dedicated "key pocket" for storing them.
  • ThanksKilling Day: There are a few doors that are locked and require a key to open in the game. These include the key to the house, and the key to a fenced in area where the axe head is.
  • Heaven Dust: Like any good Survival Horror game, this game is full of locked doors that require their designated key to open.
  • Colorgrave Universe:
    • Featured all over the place in Prodigal, being a game that consists mostly of dungeons. In the post-game and New Game Plus you can progress a bit faster by purchasing Normal Keys, but these can only get you so far because some places have Crystal Keys, which you have to move from one place to another without taking any damage at all or it will break (thankfully it respawns so you can keep trying), and Daemon's Dive has Divine Keys, which can only be found within that particular dungeon to stop you from relying on Normal Keys that were acquired elsewhere.
    • The Crystal Keys make a return in a few levels in Curse Crackers: For Whom The Belle Toils, as well as regular keys which won't break but you will lose them if you die. Once you reach Grevenfel, you can buy a key from Elinore's shop to open any lock, but like with all items you can only have one at a time.
  • Bram The Toymaker: The house has its share of doors that are locked and need a key to open. Some of the doors are coloured a certain way, and will only unlock when the corresponding key's used in it.
  • Observo: The game, being a love letter to Survival Horror video games of the 2000s, is full of locked doors that need the corresponding key to unlock.

Non-Video Game Examples

  • Commonly used in the Fighting Fantasy series of Gamebooks. Most of the time gameplay would revolve around obtaining Item A to get Item B, then using Item B to get Item C and so on...
  • In a rare non-Video Game example, the 'Tomb and Trap' chapter of Various Vytal Ventures features an exercise to gather relics of seemingly odd shapes that are later revealed to fit together... and act as a key to the only exit.
  • In Girl Genius the fragmented AI of Castle Heterodyne tasks the prisoners trapped in it to work on repairs with tasks like this on occasion by locking them in a room or wing of the castle and not letting them out until that section is repaired. Due to the state of the castle, the fact that there is no way to get food to individuals trapped in this manner, and the fact that the castle just can't pass up the opportunity to murder its occupants in amusing ways this often leads to the deaths of all involved rather than any repairs and opened doors.
  • A major mechanic in the Zaltec series of gamebooks. The puzzles don't have an explicit "if you have item X, you may proceed" condition but rather the items are parts of visual puzzles that can only be solved once you've actually seen the item, thus preventing cheating (and serving as an actual puzzle).