👉 A library is a GnollHack special room with bookshelves, spellbooks and scrolls, guarded by one of four groups of monsters.
Libraries are generated at random from dungeon level 8 down. The floor is parquet. One square in five has a bookshelf, and of the other squares, one in five has a spellbook or a scroll lying on it (one in four from level 12 down). About a quarter of these are spellbooks, which makes a library worth finding for a spellcaster.
Each square has a 1 in 2 chance of a monster, so about half the room is occupied. The group depends on the depth:
| Dungeon Level | Group |
|---|---|
| 8–9 | Gnomish wizards or gnoll wardens, equally likely |
| 10–12 | Liches (1 in 2), gnomish wizards (1 in 4) or gnoll wardens (1 in 4) |
| 13 and deeper | Liches (3 in 4) or tentacled ones (1 in 4) |
The monster in the middle of the room, if there is one, leads the group: a gnoll supreme warden for the gnoll wardens, and a demilich instead of a lich for the liches from level 13 down. A lich group is mostly imps and quasits, with some liches among them. Tentacled ones are GnollHack's mind flayers.