Deadweed Cavern is an underground mining cavern with Dark Water located beneath it.
Deadweed is an old Cavern for gold mining, and is now owned by Dr. Blakk. He uses it to get his dark water which he uses for ghouling Slugs. Miners once mined there but were exposed to dark water, causing them to become ghost-like creatures that scared away anyone one who tried to visit the cavern in order to protect others from suffering the same fate.
This cavern is home to Frightgeist Slugs.