The party is ambushed by necrotic spiders and undead in the egg-shaped chamber on the Underdark side of the portal. Defeating these creatures, they walk up Set’s Shadow Bridge to the only exit and proceed through the tunnels.
They find their way blocked by water. Set performs a ritual allowing everyone to breathe water and move freely through it. Walking along the bottom of the watery tunnel, they come to an underground lake. Defeating the kuo-toa guarding it proves difficult because of the lightning moss growing along the shore.
They cross another Shadow Bridge to escape this chamber after looting the fish-men.