The door vault is a particularly infamous and deadly vault. It can appear in D:15-27, the Vaults, the Elven Halls, Hell, the Crypt, or the Realm of Zot, and can appear multiple times. It consists of a 10x10 square that is entirely made up of doors, except for the innermost 16 squares, which contain nasty out-of-depth monsters.
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The monsters at the center of the vault will be appropriate to the branch you're currently in. For Vaults and the main dungeon, this means standard out-of-depth monsters: the crowd you'd usually see around D:27, including such nasties as shadow dragons and titans. The other branches have more specific monster sets:
- Elf: What you'd normally see on the last level of the Elven Halls: deep elf blademasters, annihilators, sorcerers, demonologists, master archers, and high priests A few of the squares might contain more normal elves, but expect most of them to be the high-tier ones.
- Crypt: Bone dragons, liches, ancient liches, reapers, with the occasional curse toe or death cob. Somewhat diluted by normal crypt monsters, but still, expect nastiness.
- Hell: Varies by branch. In each case there is a small chance (generally less than 20%) of a square containing a normal monster for the branch and depth.
- Tartarus: Shadow fiends, shadow dragons, liches, ancient liches, reapers, soul eaters.
- Cocytus: Blizzard demons, ice fiends, frost giants, simulacra, occasional titans.
- Gehenna: Brimstone fiends, hellions, balrugs, fire giants, occasional hell sentinels.
- Dis: Any fiend, hell sentinels, tormentors, iron dragons, iron golems
- Zot: Expect to see many non-base draconians, in addition to orbs of fire, death cobs, Killer Klowns, electric golems, and even the occasional curse toe or ancient lich.
This vault is a major reason to learn travel exclusions. Luckily, the game will alert you to the presence of "a strange structure made of doors" when this vault comes into view. Unfortunately, excluding it is not necessarily enough: it is still quite possible for some interloping monster to open the doors and release the monsters all over the level. There is no particular way to avoid this, sadly.
Be aware that if you see even one monster that you suspect is from this vault, all of the monsters inside have likely been released. If you can't handle them all, get off the level. In fact, the presence of this vault is usually good enough reason to skip the level anyway: the more time you spend on a level containing it, the greater the chance some kobold will come along and open it.
There is no reward for this vault other than the experience gained, and any items the monsters might have been carrying. It can be a useful way to gain experience, but be very careful: just because you can handle the orc warlord that came out of it doesn't mean you can handle the shadow dragon that's lurking around the corner.
Avoid this vault like the plague if you see it in Hell. It is quite likely to contain multiple torment-capable monsters, which can spell a very quick end if you confront them all at once. One should always be moving in Hell anyway, and a Hell-placed door vault is yet another reason to do so.
In 0.12, these doors will all be visible from the start, and the outermost ring of doors will be runed doors, preventing auto-explore or monsters from opening them.
This vault has been taking out players for many versions now. In older versions, though, it was somewhat kinder when it appeared outside of the Vaults or the main Dungeon, tending to contain monsters that were simply appropriate to the branch end. However, the game itself did not provide any warning as to the vault's nature, and preventing autoexplore from opening it would require manually excluding all of the outermost still-closed doors.