From Dragon Eye Atlas

Dohelrus is a famous ruin and dungeon south of the city Rocca, one of several well-known ruins in the area. It is located at the end of a valley and is widely assumed to have been a temple of a long-forgotten religion that appears to have worshipped a snake-god of some kind, as images and statues related to snakes can be found everywhere within.

The Dungeon of Dohelrus

While a good-sized building on the outside, a hidden passage discovered only in 52 AV leads underground along a winding, downward-sloped path until it terminates in what appears to be a series of natural caves. These caves are infested with vermins, spiders and other creatures, but pose no real danger to any halfway experienced adventuring party.

However, in the third cave, a magical door leads into the real dungeon. The door only opens when given an infusion of mana in the shape of a thimble of blood from a willing, spellcasting humanoid. Beyond it is what must have been the inner sanctum of the snake cult, with a main chamber, living quarters and other side chambers, but also a cell complex that hints at human sacrifices.

This first level is well explored, and aside from occasional undead (often the re-animated remains of parties that perished here) and a number of traps that seem to reset by themselves, holds no major threats and no longer any treasures. It is also well explored and merchants in Rocca sell maps of both the caves and the inner sanctum.

There is, however, another hidden passage (discovered in 59 AV) in the back wall of the main chamber, leading deeper. It is rumoured that few who venture there have returned, and those that do refused to speak about what they found.