The Gantry of the Abyssal Well in Entry hall 920 was a huge, circular cave lined with plates of corrugated copper, suspended high above a yawning upright shaft fifty arm-lengths in width. The shaft dropped straight down into the black heart of the mountain, venting a freezing draft that smelled of ancient machine-oil, hardened seaweed, and crushed magnetic iron. Every surface in the cave was damp with water drops, and the copper wall-plates were coated in a fine, emerald patina of green rust that tasted like dry metal on the lips.
Hanging from four huge chains of star-fallen iron in the center of the overhead frame was Obsidian Diving Bell Number Three.
The vessel was a sphere of tough, brutal shape, twelve feet in width, cast from an alloy of meteor-iron and fiery black glass that had been cooled in baths of whale oil under thousand-ton high-pressure presses during the First Dynasty. Its surface was not smooth. It was faceted like a dark, unpolished garnet, each three-sided facet three inches thick, secured to its neighbor with double-riveted straps of cold-hammered bronze. Around its equator ran a heavy rub-rail of stone-hard hardwood three feet wide, designed to fend the sphere off jagged underwater reefs. Meanwhile, the lower hemisphere was weighted with thirty tons of lead ballast rings held in place by magnetic trip-dogs.
