Cavernous levels are levels that feature large circular rooms occasionally interspersed with short connecting corridors. Cavernous levels tend to be considerably more dangerous than normal levels because monster generation rate is much faster, and it is easy to get surrounded.
Most dungeon features cannot occur in cavernous levels; the exceptions are altars, ant nests, beehives, herbs, and open threat "rooms" — i.e. threat rooms that happen to lack the actual walls holding the monsters in. Threat rooms in such form are much more dangerous than on normal levels: they feature a large (often 25-40) number of levelled creatures of the same type that will engage the PC once spotted. Due to the large numbers and close proximity of monsters, and the open spaces, they can be very difficult to handle — particularly if the denizens of the open threat rooms are summoners, vortices, or otherwise dangerous monsters such as diamond golems.
Although the design of cavernous levels is not fixed — they appear to be modified regular levels — their locations generally are. The following is a list of all cavernous levels in ADOM:
- The fifth level of the Puppy Cave
- Levels 3-5 of the Hall of the High Kings
- Two levels of the Caverns of Chaos, typically around D:37 and D:44.
- All levels of the Blue Dragon Caves
- All levels of the Scintillating Cave except for the last level.
- Levels in the randomly positioned Putrid cave (some or all may be cavernous).
The Big Room shares the main features of cavernous levels — wide open spaces and high monster generation — but is not a proper cavernous level because of its fixed, clearly non-natural size and shape, and the guaranteed presence of herbs (with the exclusion of other dungeon features).