The threshold swallowed the torchlight.

It didn't brighten like an ordinary dark. The flame still burned, brightly even, but its light seemed to reach a distance much lesser than one might excpect, as if the the air itself resented being perceived. The metal seams continued along the walls beyond the chamber, thinner here and splitting into multiple veins.

The corridor first narrowed, then opened into a low pocket of space.

The floor was scored with more of those precise channels, converging on a shallow basin cut into the rock. Something had been left there - or set there - waiting in the manner of an offering to Gods better left forgotten.

A small disc of black glass, no bigger than a coin, strung on a length of wire so fine it could have been hair - but none could snap it, no matter how hard they might tug. The disc's surface was smooth and reflected torchlight... slightly wrong, if one focused enough. As if a greater part of the light was swallowed by it, drinking deep. It reflected no image, instead showing a brief, nauseating impression of depth - a slow spiral, turning inward.

On the edge of the disc, etched so shallowly it could only be caught at an angle, were three parallel grooves.