Deep Horizon, adventure for D&D 3rd/3.5th ed, by Skip Williams.
“A series of earthquakes and eruptions have rocked a normally placid land. Strange creatures sighted in the dark of night raise fears across the already disturbed countryside. As tales of a lost race that once warred with the drow begin to surface, only the boldest adventurers dare to descend into the shadowy darkness.”
Stand-alone adventure for 13th level characters.