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, the outermost layer of which are runed doors. The innermost 16 squares contain many nasty out-of-depth monsters. There is no increased chance of loot within.
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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.
Prior to 0.12, the outermost doors of a door vault were hidden rather than runed. This meant that wandering monsters could and would happily open the vault for you, releasing the contents for you to encounter as you explored the floor.
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.