Iron doors should be able to take water damage and become rusty. Once rusty, it should be possible to break an iron door like a normal wooden one.
Alternatively, iron doors should be corrodable by throwing or smashing acid on them, with it taking 2-3 potions to weaken a door to the point of destroyability.
Priests tending an altar should repair the walls and doors of their temples if they are damaged, like shopkeepers do. (In NetHack 3.7, peaceful monsters avoid digging temple walls, but the temple can still be damaged by other monsters or the player.)
Physical explosions (those from a gas spore) should blow away doors that are in the blast radius.
If you open a door that turns out to be a mimic, it “falls on top of you” and deals damage in addition to sticking to you.
If you use #force when standing next to a closed door that you don’t know to be unlocked, the game will ask if you want to force the lock. If you say yes, you try to; if the door is actually unlocked, you’ll get a message indicating that and “You decide not to force the issue.” If it’s locked, you try to force the door with your weapon, which could involve prying with a bladed weapon (opens the door quietly and faster than kicking, but higher chance of breaking the weapon than forcing a container would) or bashing with a blunt weapon (much the same as kicking).
Artifact lock pick Doorbane, which mostly works like a regular one but prevents doors from resisting when it’s carried.
This functionality should also probability extend to the Master Key of Thievery.
Instead of making all trapped doors explode and stun the player, add more varied door traps. The trap should be determined based on depth. It should also be selected deterministically based on the coordinates of the door (a convenience so that a trapped door will always have the same trap effect without having to store which trap it is.)
Additionally, new traps can also be used with more door states, rather than have all traps trigger by trying to open the door. Nondestructive traps could also remain on the door until the door is untrapped, rather than vanishing.
An interesting addition would be if doors were made restrictedly or completely untrappable, in order to prevent optimal strategy from being attempting to untrap every door that the player comes across. Or possibly an attempt to open or close a door should do a cursory trap check.
List of door traps in rough order of minimum depth necessary to generate them:
A “lignivorous” flag that can be specified on a monster species. Lignivorous monsters can eat wooden objects and doors like metallivores can eat metal objects.
Artifact key that creates a door in a wall wherever it’s applied. (Unless the wall is nondiggable?)
You can apply a can of grease or potion of oil to a door to guarantee that it will close and open without resisting.
Amorphous monsters that are huge or gigantic cannot squeeze under doors, or through iron bars.
Giants can rip doors off their hinges, by picking them up, to use them as weapons. They do a lot of damage, and can only actually be wielded by giants. Possibly, kicking a door with excessive strength (and/or being a giant) not only breaks it off the hinges, but sends it flying to hit anything unlucky enough to be in its path.
There isn’t really an obvious object class for a ‘door’ object to be in, though WEAPON_CLASS is probably the most straightforward.
Possibly also allow this with sinks or trees. All of these heavy improvised weapons should probably use club skill.
When a door is hitten by an opening beam, it actually opens, rather than becoming unlocked. Also, any doors adjacent to it will also be opened (for the “double doors” that appear in some special levels).
You can use #force to pry open doors with edged weapons; however, this requires more Str and has a higher chance of breaking the weapon (perhaps dependent on the weapon’s weight.)
When you kick a door that is closed but not locked, it can just crash open and become an open door instead of breaking. This is only if you kick it in one specific direction, deterministic based on its coordinates. Diagonal kicks can count as kicking in that specific direction, but kicking perpendicular or opposite will result in the door breaking like usual. If you kick open a shop door like this and don’t destroy it, the shopkeeper yells at you a bit but doesn’t demand money.
Doors are much less likely to resist when trying to close an open door.
The cost of breaking a shop door is at least partially non-deterministic, so you can’t figure out the exact amount the shopkeeper will demand in advance.
Instead of storing door traps as part of the door state, use the trap field of struct lev with a special new DOORTRAP trap to indicate that there is a trap on the door space.
Certain special rooms (typically ones that have awake monsters in them that shouldn’t wander around the level) always generate with all of their doors locked.
Throne rooms generate their monsters awake, but also generate all their doorways as locked.
Open doors can generate trapped. When you step off an open door to some other space, it closes and locks behind you.
Iron doors, which generate 30% of the time a normal door would be generated on dungeon levels 7 or below. They use the symbol +. They work the same as normal doors, but they cannot be burned, kicked, or blasted down, or destroyed any other way. If one happens to be locked, you have to unlock it “properly”.
At high skill, the spell of wizard lock forces items off the doorway to adjacent squares so it can make the door. If there’s a monster on the door, it also gets forced off to an adjacent square, or becomes embedded in the door if none exists.
Zapping an opening beam at a closed, unlocked door opens it. Casting knock at Skilled or Expert lets you unlock and open all at once.
Every lock in the game has a deterministic chance (based on object ID if a box and xyz coordinates if a door) of being unopenable by a credit card. Attempting gives the message “It doesn’t look like this lock can be opened with a credit card.”
Zombies can’t open doors, but if there are multiple adjacent zombies on one side of a door, they can bust it down.
Rock moles (and other tunneling monsters?) can’t eat through wooden doors.
Gelatinous cubes can eat wooden doors in their path.
Pressure plate traps that cause all the doors of the current room to close and lock (doorways without doors could turn into iron bars or, on deep enough levels, all doors could turn into iron bars). Triggering this automatically removes the trap. Generated very rarely, and has special generation that occasionally makes it appear just inside a door to a throne room.
Bringing back different types of keys for different sorts of locks. This is not the old random key shapes and random lock shapes system; the discussion concluded that special keys should be used for a few specific purposes: game progression, a one time use reward, or some non-unique type of door where each key is one-time use or limited use. In particular, this third one could be used in Gehennom to block off areas, with “soul keys” or something similar that open special doors there and are generated with demons. Gehennom doors could also involve a blood ritual requiring some sort of expenditure of resources or damage to the player.
Turn kicking a door into an occupation: you’ll keep kicking it until you get interrupted somehow, or successfully kick it down.
The travel command automatically opens doors as you go.
If you have very high strength, kicking open a door can cause it to be knocked off the hinges and land on top of a monster behind it.
Glass doors that you can see through and kick to break with ease.
If polymorphed into a giant, you can pick up a door off its hinges (breaking it).
Turn trying to open a door into an occupation: if you get attacked or otherwise distracted while trying to open the door, you will stop, but you don’t have to manually keep trying and failing to open it.
Kicking down doors exercises Str and not Dex.
You can engrave on walls or doors. Elbereth on walls or doors doesn’t work. You can read it by standing on the nearest space. Random graffiti, if it generates on a floor square next to a wall or door, may say “Something is written on the wall here.” instead of the floor. Graffiti could render as ~ or something similar.
You can walk diagonally into or out of an open door if there is also another open door adjacent to both your starting and ending location.
Allow edged weapons to be applied to force open door locks. (They can break in the process of doing this.)
Kicking down a door may damage a creature standing on the other side. This is guaranteed if you are wearing kicking boots.
