From publisher blurb: A 5th Edition Mini-Dungeon adventure for 4-6 PCs of levels 10-11 Deep in Underworld, near the outlet of a sacrificial wellshaft, the PCs find a colossal cavern full of densely packed mosses, liverworts, ferns, and bioluminescent fungi including many Armillaria and Mycenoid species. A sanctuary was created by survivors before they moved on, with corridors and rooms carved from the living biomass. Historically, the walls, floors, and ceilings were kept smooth, but Nature’s returned; now they’re unkempt, with vermin, animal, active plant, and other pathways pitting them. It’s unclear if the area is at “ground level” - in fact, it’s hundreds of feet above the cavern floor.