The Lost Treasure of Atlantis

From publisher blurb:

An adventure in Hyperborea designed for from four to six characters of 6th through 8th level

In the far reaches of Hyperborea's Crab Archipelago lies a small, mountainous island known as Crystal Point. Passing sailors recently have witnessed a crimson glow in Crystal Point's waters and beams of russet light shining up from its steep cliffs. Too, unusually frequent lightning storms in the area have torn the sky in blinding flashes, shattering the air with their awesome sound. The seedy wharf taverns of Khromarium and elsewhere buzz with these strange tales—some even speculate that Crystal Point may hold the lost treasure of Atlantis!