This design was inspired by Goblin Gully, a neat one page dungeon adventure by Dyson Logos. The original uses a strictly vertical section map to describe a sealed horror lab of a forgotten culture. The upper levels of this slave pit have lately been taken over by goblin raiders, who are however still unaware of the dangers lurking below their hideout.
The cornerstones of original setup are still present: focus on verticality, a rope bridge spanning the central ravine as well as the dark pool with eldritch horrors deep below. Some room ideas also made it into this revised version, such as the passage through the monster’s jaw or the manhole above the altar chamber, allowing the goblins to stage a surprise attack.
I did a new completely new, revised map, added lots of new features and changed the focus of the ruins towards a serpent cult. I figured as Alfheim features a strong links to the ancient serpent men (which again are plainly derived from Howards Conan and thus Lovecraft’s Yig), it might be a good fit here.