The Winter Eye Combination

You enter a circular chamber of blue-black stone where frost feathers the walls despite the still air. A waist-high pedestal stands beneath a suspended crystal lens, and three silver rings around its sides slowly rotate by themselves with a sound like distant ice cracking. An owl, a snowflake, and a black moon are carved above the sealed doorway, but each is crossed by a thin line of tarnish. The floor mosaic glimmers whenever the rings pass one another, and somewhere inside the walls, a slow heartbeat answers every click.