We return to Shadowdark environmental threats by delving deeply into underground hazards. Among the dangers we discuss are collapsing tunnels, fungal forests, and the fun-but-dangerous Goonies-style water slides. Inspiration for these threats comes from Ken's Mörka Norden campaign, which features a Viking-inspired alternative universe ... and a trek underground to explore the "Deep Crawl" in search of the nefarious Rat King.