The Wavestone Monolith

An entry in the tenfootpole Wavestone Keep contest! From the publishers blurb: Fear the silence, the water, the dark stone itself! Deep within the sweltering jungle, a monolith of black basalt floats upon an undulating lake hidden in a cave. They say inhuman howls emanate from it on moonless nights... and that the fat gems and coins of a lost society lie inside for the taking!