This is a downward-extending branch consisting of between 25 and 29 levels; it is the branch in which the player begins the game.
The following dungeon branches connect to the Dungeons of Doom:
| Elemental Planes | (DL 1) |
| Gnomish Mines | (DL 2 to DL 4) |
| Sokoban | (DL 6 to DL 10) |
| The Quest | (DL 11 to DL 16) |
| Fort Ludios | (DL 11 to DL 27, not guaranteed) |
| Gehennom | (DL 25 to DL 29) |
The following special levels may be found in this branch:
| Top Level | (DL 1) |
| Oracle | (DL 5 to DL 9) |
| Big Room | (DL 10 to DL 12, 40% chance) |
| Rogue Level | (DL 15 to DL 18) |
| Medusa's Island | (2nd to 5th level from bottom, DL 21 to DL 28) |
| The Castle | (Bottom level, DL 25 to DL 29) |
(Note that some level ranges are interdependent, so certain combinations of branch/level locations are impossible; for more specific information, see individual entries.)
Most non-special levels consist of an "ordinary" room-and-corridor layout; some rooms may be special (see room-343.txt). Levels between Medusa's island and the Castle have a 4/5 chance of being mazes. All non-special, non-branching levels below DL 3 are eligible to leave bones files (which may result in maze levels being encountered outside the range just noted).