kwynn89,715 Locked 31 Jan 2019
In the Rotting Croplands you'll come across the Royal Hive. Inside the Royal Hive are the Queen's Lair and two additional cave entrances. On the overhead map they are labeled as Dermapteran Tunnel Entrance. One of these is the side area the Skittering Den and in that area you'll find a section of the wall that can be broken and that area contains another cave entrance to the Den of the Lost.
Gollus is in the Den of the Lost and unlike other boss creatures he does not have a star over his head (at least he didn't for me). He uses poison and he has a chance to drop a nice ring.
There is also a desecrated shrine in this area that requires you to kill a wave of Riftspawn.