The Witness in Three Movements

You enter a circular vault of black stone slick with cold moisture. Three symbols are carved into the sealed door: an open eye, a twisting spiral, and a tooth-filled maw. Violet light leaks through hairline cracks in the walls, pulsing in time with a wet, distant heartbeat. At the chamber's center, a glassy orb turns its pupil toward each of you. Three dark crystals rest in shallow niches, and a bronze tablet hangs above them, its letters rearranging whenever nobody is looking directly at it.