Dark: Gloomy, shadowy, pitch-black, impenetrable, dismal
Eerie: Unsettling, ominous, haunting, foreboding, chilling
Dangerous: Treacherous, perilous, hazardous, unstable, menacing
Mysterious: Enigmatic, concealed, hidden, secret, unexplored
Devoid: Barren, empty, desolate, lifeless, silent
Other: Damp, cold, dripping, mossy, claustrophobic