Locked Door

"You need a Level 13 Quest Key to open this flimsy wooden door. Would you rather just kick it open? I mean, I really don't see why you should have to go try and fight that giant dragon and shit when you could just open it with your hands. The wood is really decomposed. But it's your choice, chief. The last two guys decided they wanted to try and get the key. Where are they now? Fucking dead."

- This picture, from Cracked.com

""They always lock the door. You’d think they’d have learned by now. Doesn’t look like there’s a key – that would be too easy. The console to unlock the door is probably hidden in some room twelve floors up or something… how does that make sense?""

- Kyle Katarn, the Chuck Norris of the Star Wars Expanded Universe.

A locked door blocks the main characters' way. However, you must go to great, irrational lengths to locate a key, and it will never be in a place you would intuitively expect to find it, given the location of the Locked Door (yes, I tried looking under the mat). Especially infuriating when the key is an extremely small unobtrusive item that's impossible to see from a distance at most screen resolutions.

Which even assumes you aren't supposed to bypass it entirely and take some other route, i.e. through the air ducts.

Of course, even if the locked door is a wooden gate with a tiny padlock on it, you can't just bash it down or blow it up. No, not even with the tac-nuke you've been carrying around.

Sometimes, the door isn't even a real door: it might just be a texture of a door to give the illusion that it's a real building / corridor, while there is no actual room behind it.

If the key is a Plot Coupon, you've got a Broken Bridge.

Compare Solve the Soup Cans. May require the attention of a Master of Unlocking, but if even he can't get past it without the key then you've got a Plot Lock.

Action Adventure

 * In The Legend of Zelda series, every dungeon (except the first three of Ocarina of Time) has several doors which can be locked by any one of several keys. There is also generally a "Boss Key" leading to the room which will contain the Boss Battle.
 * And how often have you been in a room with doors that cannot open until all monsters in the room are dead? Or, for that matter, rooms where the doors don't open until we locate the gerbil that escaped, or the door that refuses to open unless all the torches in said room are lit...
 * From the Master Quest expansion, cow-shooting. Yes. Shoot a cow, open a door.
 * Searched everywhere for that key in the Forest Temple in Ocarina? Yup, it's in the most obvious place, involving walking outside the temple, climbing a tree, jumping to another tree, and opening a treasure chest... Which of course begs the question "Why are keys inside of treasure chests?"
 * Phantom Hourglass parodies this a bit: the "Boss Key" is so huge that it actually slows Link down as he has to lug it all the way to the door.
 * Not to mention doors in some of the towns that are always locked and you'll never be able to get into. This mostly happens in the N64 games.
 * Oddly enough, in Castle Town of Ocarina of Time, during the day, one of the doors in the back alley is locked. At night, it's open, and you can enter, but no one is home. If you want to talk to the person that's there, you have to go inside at night, play the Sun Song, and then the guy is there. The worst part? He doesn't have anything important to say.
 * Killer 7 has its share of locked doors, but no keys or alternate routes. The trick? One of the playable characters (which you can freely switch between) is a thief.
 * Though not very door-like, the Barrier Glyphs in Ecco the Dolphin fill the same function. It's also a somewhat cheeky example, since there's clearly enough space around any given crystal for Ecco to squeeze through. There's a tool-assisted speedrun of the first game out there wherein the player actually manages this. Repeatedly.
 * Cave Story likes using locked doors to obstruct the player's progress. One door is rusted shut and has to be blown up -- but first, there is a Fetch Quest which involves getting a key to open another locked door. In the Fan Remake, you actually get to open this door with your missile launcher instead of finding its key.
 * In Evolva, starting from level 7, you'll need to find some coloured disks (either lying on the ground or dropped by enemies) that serve to open the doors with a circle on its top of the same colour.

Adventure Game

 * Riven partly subverts the latter variety: at one point you find a locked door, incapable of being opened by any means ... and can simply crawl under it.
 * Shivers was set in a museum, all of whose doors were controlled by nearby logic puzzles. In context, this was not entirely unreasonable, as the setting was meant to be a sort of puzzle theme-park. The sequel, however, is set in a town where almost every door is similarly locked. The player even encounters a diary with an entry deriding a "newfangled lock" (that is, the kind that actually uses a key).
 * Parodied and defied in Discworld II. Rincewind, upon encountering a locked door, launches into a tirade about how he'll be expected to go on a series of Fetch Quests to persuade a character to give him the key, and eventually demands that the bearer of the key just hands it over to him. He does, only for it to be revealed that the locked door was on a false wall around which Rincewind could simply have walked.

First-Person Shooter

 * Half Life and its sequels tended to hang a lampshade on the second variety by mentioning a backstory in which protagonist Gordon Freeman and Barney Calhoun usually competed for who could find the most interesting way to retrieve Dr. Kleiner's keys when he locked himself out of his office. It also had the former category as well, with some doors locked with retinal scanners Freeman himself isn't cleared for.
 * Parodied brilliantly (along with the Insurmountable Waist-Height Fence) in Concerned.
 * 'White picket fence' (and 'tuft of grass') being, of course, a reference to Smurf Rescue.
 * However, while doors are indestructible, tiny padlocks can be shot or bashed.
 * Usually, if you end up on the other side of a locked door, it will open from that side, creating a Door to Before. Not all that helpful in a primarily linear game though.
 * Deus Ex: Many locked doors have a strength value along with a lock value. Strength value determines how much punishment they can take before breaking, whereas lock value determines how many lockpicks you'll need to open the door. You could also just find the key to the door to open it as well. There are some doors that are unpickable and indestructible, and require a key to open, or for the player to find an alternate route.
 * This holds the same for Deus Ex Human Revolution, except all doors have keypads now, and there is not a mechanical lock in sight, so no lockpicking. They can still be blown open with explosives. Most of them anyways.
 * Star Wars Jedi Knight: Jedi Academy: at one point, when faced with a Locked Door, Kyle Katarn, who has starred in this sort of game before, snidely comments to the player character, "They always lock the doors. You'd think they'd've learned by now." and later, "The console for opening the door is probably hidden in some room twelve floors up ... how does that make sense?"
 * Mildly subverted in Dark Forces II: Jedi Knight, where in one town there is a locked door that Kyle cannot open at all, even with a lightsaber. But a random citizen of the town comes out of the door. If timed right, it is possible to get into the house when the door is opened,
 * Lampshade Hanged in Serious Sam and Serious Sam 2. NETRICSA sometimes makes references to this.
 * In Serious Sam 2, Sam, after encountering another locked door and after NETRICSA's announcement of that, says "If I had a dime for every key I found.".
 * Subverted in the hybrid FPS/driving game Redline, where doors generally aren't an issue as the whole game takes place in a post-apocalyptic wasteland. At one point, though, while infiltrating an enemy base you come across a locked door. Instead of wasting time searching for a key, Mission Control just tells you to blast it down with a rocket launcher.

Hack and Slash

 * In Diablo II, while not necessary to the plot, locked chests required generic keys to be open. The hero, despite having the strength to vanquish the three prime evils, is incapable of opening these chests without a key.
 * Fable gets worse about this with every game. In Fable I, only large doors were impossible to bash open and even those could often be picked. In Fable II', the stealthy option is eliminated, but they can still be forcefully bashed open. In Fable III'', your monster-killing, nigh invincible hero must politely knock and hope for a response.

Interactive Fiction

 * The Interactive Fiction game Bureaucracy, written by Douglas Adams (of Hitchhiker's Guide to the Galaxy fame) features the oddest method of getting through a locked door ever seen in a computer game.
 * Metal Gear Solid 3 has a similarly tricky door. Just remember to disguise yourself as a scientist before attempting it. Or hide.

MMORPGs

 * In City of Heroes there are -- incredibly rarely -- locked doors during instanced missions, where the player needs to defeat a specific random enemy to receive the key. Most people tend to defeat every enemy they see anyway, so it's not really a problem.
 * Perfect World has some dungeons where the door will not open unless you kill a miniboss. The first time this takes place, it's in the level 29 dungeon Hall of Deception, and it appears very frequently afterwards.
 * There's a lot of Locked Doors in World of Warcraft, mostly dungeon doors. Those require specific keys to open, which are obtained from various sources, such as quests or loot from mobs. Alternatively, most of them (but not all) can be opened by a Rogue with high enough Lockpicking skill, by a Blacksmith's Skeleton Key, or an Engineer's Seaforium Charge. Also, in order to prevent people from not being able to resurrect, dead players' ghosts CAN walk through these doors, which makes it possible for some dungeons to be accessed without a key, blacksmith or engineer.
 * All of these doors also have a lever on the opposite side, allowing a non-rogue, engineer or blacksmith to leave. On busy days, and especially before expansions when it could take ages for people to gather for a dungeon, it was sometimes possible to get in by just waiting around at the door until somebody else wanted to leave.

Platform Game
""Somebody's gonna pay for makin' me find these mother(beep)in' keycards!""
 * In Duke Nukem: Manhattan Project, the forcefields are deactivated using keycards. Duke's responses to the players attempts to deactivate these fields lampshade this trope; he complains about having to find keycards to open doors to finish levels, which has been standard of the Duke Nukem franchise since the original PC trilogy.


 * In Billy Hatcher and The Giant Egg, you're going to find a few Locked Doors/Gates in almost every mission of the game. However they're not as bad as other examples, as they're generally opened by either hitting a nearby switch, defeating all of the nearby enemies, or (in a few rare cases) using a Rabbish to activate a pair of lights by the door.

Puzzle Game

 * The 7th Guest (and its sequel The 11th Hour) is duly infamous for taking the similar tack of unlocking doors in response to the player solving a totally unrelated set-piece Solve the Soup Cans puzzle somewhere else in the room, such as a game of "Lights Out" with bizarre triggers. The game would also re-lock some doors depending on how heavily the player abused the in-game help guide in order to skip puzzles altogether, sometimes making the whole game flat-out Unwinnable.

Roguelike

 * Averted in Nethack, where any skeleton key can be used to unlock any door, and any door can be bashed down if the character is strong enough (though bashing down a door makes noise which can alert nearby monsters).
 * In Slash EM, one of the three items necessary to complete the game is behind a series of unbreakable doors which can't be opened by ordinary skeleton keys, requiring the player to possess two out of the three artifact keys to get past them.

Role Playing Game

 * With The Elder Scrolls IV: Oblivion, no matter how physically powerful a character is, how big his or her weapon or powerful his or her spells, a locked door is indestructible. Some indeed require a specific key, although most can be picked, magically or with actual picks. Several ruins have doors which are opened by pressing a block on the wall...somewhere in the ruin.
 * Daggerfall locked doors could always be bashed open, usually to the cacophony of "Halt Halt Halt" if your character was in a city or house at the time. It couldn't be helped, though, because your lockpicking skill was crippled and there were no keys in the world.
 * Mostly averted in the Ultima Underworld games. Sturdy doors can be bashed, lockpicked or opened by magic, bypassing the need for the key. Massive doors cannot be bashed, but only a few cannot be lockpicked or magically opened.
 * In Ultima VI one could blow up even plot relevant doors with a powder keg, unless they were magically locked which merely required an "unlock" spell. Interestingly, even with non-pickable key-specific locks; one could cast the "lock" spell and then the "unlock" spell to open them without destroying them or hunting down the key.
 * In the original Pool of Radiance many locked doors could be opened with lockpicks, with the Knock spell, or simply by bashing them a few times.
 * In the Avernum series almost all locked doors could be picked open, naturally or magically, or bashed open. Some, however, required a lever/switch/button to be pushed/pulled, or a special item to be unlocked. The levers were usually in a place that makes sense, close to the door with easy access for those who should be there, but hard to get to if you shouldn't be.
 * Unlock Doors at level 3 opens everything that has a door script on it.
 * In Star Wars Knights of the Old Republic and its sequel characters can both pick locks and use weapons to bash the lock of a door open. However, there are still some doors that cannot be opened in either way, such as the entrance to the Black Vulkar base on Taris, resulting in a long tedious sidequest involving a Twi'lek and her Wookie friend.
 * After the End of the world in Final Fantasy VI, every single door in Narshe is locked... even though there are only two people left in town at all. You can't even find keys for them, but you can look for a master thief treasure hunter to pick them for you.
 * Mostly played straight in the Fallout series, which often makes it infuriating when coming across doors you cannot lock pick. Instead, you have to find the key for the door, which may be located in a completely unmarked area on the map, if the NPC decided to get themselves killed wandering around out there. In most areas of the earlier games, explosives are a good alternative. Looking to get the T-51b armor in Fallout 3? You're going to need 3 keys to access it.
 * In Mama Dolce's there are two very hard locked doors there which lead to
 * In the first two installments, some doors could be opened by brute force and/or explosives.
 * In Final Fantasy III, although there are some locked doors, by simply putting someone with 'thief' as their job at the head of the party, they can pick the lock, and get through.
 * Sweet Home has a few locked doors that Emi can unlock, a few that require special objects, and a few that lead to nothing and aren't meant to be opened at all.
 * In Arcanum lockpicks and lockpicking spells work on most doors (and chests). Sledgehammers or axes are also effective for characters with high strength, and tech-savvy characters
 * In Lands of Lore: The Throne of Chaos, most locked doors require a key to get through. However, there are some that can be lock-picked open if your Rogue skill is high enough. Similar to the Silent Hill example above, if "you failed to pick the lock", you can always try again; if "there is no way to pick this lock", you need a key. There are even a few areas in the game where you're required to break through walls to proceed. Also, treasure chests can be bashed open with a weapon, but doors can't.
 * All locked doors in Tales of the World: Narikiri Dungeon 3 can be opened by using a Lockpick Set item or by the main characters in a Thief costume.
 * Pokémon has keys in most of its games. Sometimes you find them lying around. Other times you have to find that one NPC who will drop it. And then there's the time where you have to scale a radio tower, then get a key to the city underground area in which case you have to navigate that, simply to get ANOTHER key, to open up a door in the same radio tower.
 * Anyone who has played Neverwinter Nights knows the dread phrase. Interestingly, one of the doors did have the key under the mat. You could literally open the door within a second of picking it up.
 * However, many doors can be 'opened' with brute force and Fireballs.
 * Dragon Quest series is known for having locked doors and chests. Different kind of keys open different kind of doors, and the highest level key can open all doors.
 * The Game Maker Unlimited Adventures has the classic key-locked doors. There are also "locked wizard" doors, which have to be opened with the Knock spell. There are also ordinary "locked" doors, which are useless--a player character must bash through or pick the lock each time (done as a skill roll), but these rolls are so easy that a locked door will stymie only the most pathetic of low-level parties, and even then they can just move away, then move back and try again.
 * Parodied in Serious Sam the Random Encounter. Sam encounters a locked door and complains about how he hates puzzles. Then he picks up the key, which is sitting on the ground nearby, and remarks that he found that puzzle quite enjoyable.
 * Eye of the Beholder has a handful of locks that you can pick, but only on the second level; and if you happen not to have a rogue in your party, the game adds extra keys so that you don't need to pick them.
 * Dark Souls might be very Metroidvania like in level and world design, but it doesn't have the permanent power ups instead using lots of keys, lots of doors, and lots of doors that can only be opened from one side (Albeit they are permanently opening). The Master Key is the only starting gift worth using as a result of this.

Stealth Based Game

 * In Splinter Cell, while many locks can be picked or forced, there are some doors which won't open because they are "jammed".

Survival Horror

 * The Resident Evil series is infamous for having maze-like layouts in every building imaginable, usually locked in surprisingly archaic fashion.
 * In RE4, padlocks can be removed with a swing of the knife and most fences can be jumped over, an exception being a certain Insurmountable Waist-Height Fence with a Locked Gate.
 * Slightly averted in Outbreak, as some locked doors can be broken open after taking a good enough beating.
 * In Silent Hill, if a door is "locked", it can eventually be opened, if the lock is "jammed" or "broken", it's permanently locked.

Third-Person Shooter

 * In Crusader: No Remorse, all but the most heavily-armored blast-doors can be bypassed by applying enough high explosives. Doing so will, however, set off an alarm and send waves of foes your way - not to mention that you may well miss other important or useful things in the areas you thus bypass. But it's undeniably realistic...
 * Since Red Faction allows you to destroy the walls, if you see a locked door, you can just blow a hole around the door and bypass it. In one scene, you are instructed to do so, but if you have trouble getting past it, the Reverse Mole will unlock the door for you. In practice the big complaint levelled at the game was that so many doors, floors, and office cubicles were made of magic stuff that's immune to your earth-shaking rocket launchers, to ensure that the player couldn't break the key-fetch procedure or run away from a boss fight.
 * Played with in MDK. Flimsy locked doors that can't be blown open, even though you're armed with nuclear weapons? Nope, here you'll find twenty-foot-tall, two-foot-thick steel monstrosities that can ONLY be opened with nuclear weapons.

Tabletop Games

 * Many Dungeons and Dragons based games give Thief/Rogue characters the ability to pick locks. This will generally let them open treasure chests or inconsequential doors. But any plot advancing doors must be unlocked with a specific key/lever that you must fight the right bad guys to get.
 * Then again, certain doors that don't advance the plot can just be kicked open by a monk... Or hacked at by a barbarian... or blasted into oblivion by a sorceror...
 * You would not believe how many Disintegration-immune doors there are out there.

Web Comics

 * Parodied in this Dueling Analogs strip.

Web Original

 * The Game Overthinker uses these as an example of how realism isn't always the best thing in games.
 * In the Legend of Zelda the Abridged Series, after getting the Mega Crush Hammer Link and Navi skip all of the puzzles and just bash open the doors with it.