With a thunderous bone-shaking boom, the two-foot-thick stonework wall of the ancient royal smelting chimney pipe gave way.
Ancient red firebrick, hardened lime mortar, and three hundred years of compacted fire soot erupted into the underground air like black gunpowder smoke.
Lu Chen and Auctioneer Yan slammed through the deep hull breach together, tumbling ten feet downward into the underground exhaust duct.
They hit the stone floor with the moving violence of an iron anchor dropping onto a granite reef.
The royal smelting chimney pipe was narrow. Scarcely ten feet wide, eight feet high, and lined with glass-fused clay brick glazed glassy and black by ages of royal coal fire.
Low-hanging hardened melted rock waste stalactites jutted from the ceiling like rotten, stone-hard teeth.
In the damp corners of the tunnel, underground sulfur fissures hissed softly, bathing the choking gloom in a sickly, pale yellow eerie glow.
The confined space transformed the shape of the battle in an instant.
