| Possibly constructed by some powerful madman, the Vaults are said to be home to great treasures. The blood spattered liberally around the entrance suggests that there is a certain amount of violence, too.
The Vaults are five levels deep and contain the silver rune, as well as the entrance to the Crypt. They can only be entered while carrying at least one rune of Zot. The entrance can be found on either level 13 or 14 of the main dungeon.
The Vaults are a convoluted 5-floor Dungeon branch filled with long, wide hallways and countless treasure chambers (most of which are unfortunately empty). They are guarded by a wide variety of late-game monsters, as well as a number of guards unique to the branch, but the promise of the silver rune of Zot, access to the Crypt, and four guaranteed treasure or shop vaults makes it well worth the hazards.
The Vaults are a sprawling compound made up of wide hallways and small chambers of various shapes and sizes, most of which are separated by doors. Composed primarily of stone, metal, and green crystal walls, only the most powerful Earth Magic specialists or Lugonu followers can expect to alter the floor plan much. Because the arrangement of rooms can be extremely convoluted, it's easy to get cut off from the stairway back up if you aren't careful; try to clear rooms methodically to avoid enemies you missed showing up when you're already half dead.
The fifth and final floor changes this pattern abruptly. The floor contains four very large rectangular chambers that take up almost the entire area, except for a cross-shaped central hallway separating them all and an outer hallway bordering everything. These four large vault chambers have openings at each corner. All three normal staircases from the 4th to the 5th floor dump you in the very center of the floor, which will be surrounded by many vault guards and other angry Vault inhabitants. Fortunately, this floor also houses an immense amount of loot and possibly shops, along with the silver rune of Zot.
The Vaults are inhabited by a wide variety of monsters (almost anything that can appear in the lowest floors of the Dungeon or the Depths can generate here) with a very diverse array of attacks, but generally speaking the biggest threat is simply getting beaten to death by sheer brute force. Stone giants, yaktaur bands, and other creatures which have high physical damage output at range are common enough, and the wide hallways and open chambers make it difficult to effectively bottleneck opponents or cut off lines of fire. Pack enemies also appear in great numbers, ranging from high-level orc bands to devastating hell knight packs, and the various guard units unique to the Vaults each cause their own issues:
p Vault guard- Plentiful lumbering oafs with heavy weapons and sturdy armour.
p Ironbrand convoker- Recalls and buffs enemy units from elsewhere on the floor.
p Ironheart preserver- Soaks partial damage for other enemies, effectively doubling their HP until the preserver dies.
Bring sufficient firepower, take your time, and be ready to take a different staircase down if the one you just used places you in a fight you don't want to deal with right away. Also, if you get hit with a Sentinel's Mark, retreat to an empty floor as quickly as possible. The reinforcements it will bring can be devastating on a mostly unexplored floor.
Do not enter Vaults:5 before you are ready for it. If you had difficulty with floors 1-4, floor 5 will probably be too much for you, and even peeking down there can be immediately fatal.
The fifth floor is an abrupt change from the first four. All of the standard down staircases to V:5 place you in the very center of the floor, with a ring of over a dozen vault guards waiting for you and several other (much more dangerous) opponents lurking right behind them. These monsters can include titans, storm dragons, quicksilver dragons, shadow dragons, and liches, along with the worst of what you've encountered on the top 4 floors. No matter what your character type may be, charging in and slugging it out is very likely to go poorly.
You should always hasten yourself (either through the potion or spell) and use various buffs at your disposal before heading down. You'll have to move fast, either to dart through the ring of guards towards a hallway, or to kill as many of them as quickly as possible.
Melee characters may be tempted to stair dance to break up the enemy as much as possible. This can work very well against the ring of vault guards below, but a vault warden sealing the staircases from the edge of your vision, a tentacled monstrosity constricting you, or a dragon trampling you away from the stairs before you can make it back up will ruin your day. Mages with level 6-9 Conjurations can usually take out a Vault Warden quickly, but that still leaves you subject to several attacks in the meantime.
Or... bring Ignition. One to two uses will dispatch the welcoming party. This is probably the safest way to enter V:5.
If you are not of the fiery kind, casting Alistair's Intoxication with clarity works well here as well; you'll confuse the majority of the guards, causing them to injure each other and leaving you free to take out the more serious threats. This is still a dangerous strategy, however, as the noise you generate will wake and lure out monsters from the four treasure vaults.
As a mix, and what also works very well for a melee character, is to bring rF++(+), waltz down the stairs to V:5, read a scroll of immolation and start whacking dudes until the fireworks go off. Since you will be surrounded and be part of at minimum 8 explosions... only do that if you have high health and good rF, but if you do, it's a blast.
Resistances are much more important on V:5 than on the floors above. The draining attacks of shadow dragons can strip away your skill levels with frightening speed unless you have negative energy resistance, the more the better. Failing that, high evasion and Repel Missiles helps tremendously. Storm dragon breath can be brutal as well without electricity resistance, which also protects against the lightning bolts of titans, but these also know Airstrike, so avoid flying in their presence. Quicksilver dragons deal severe damage regardless of your defenses and can dispel any buffs you might be taking advantage of, so try to make them a high priority. Packing some fire and cold resistance on top of everything else is advisable, as there are plenty of other dragon types around, not to mention casters with broad spell lists.
The worst possible thing that can happen on Vaults:5 is to receive a Sentinel's Mark. If this happens, quaff a potion of cancellation, breath on yourself if you're a Purple Draconian, or quickly retreat up the stairs to Vaults:4.
Prior to 0.14, it was not necessary to obtain a rune of Zot to enter this branch, and its entrance was located on D:15-20. Also, the four chambers on Vault:5 only had entrances on the corners nearest the center of the floor.
Prior to 0.12, the Vaults were made up of 8 floors, the first 7 of which were all wide open areas spotted with rectangular rooms. Also, the vault guard was the only guard-type monster found here, and they usually appeared on the eighth floor.