The armored bronze portal of Entry hall 732 swung open into an extraordinary underground castle: The Submerged Bastion of the Outer Defenses. Carved directly out of the oceanward dark rock doorstep during the earliest decades of the First Epoch, this huge stronghold was designed to serve as the unbending anchor of the entire safe hall. It took in both the crushing deep water pressure of the deep sea and the violent percussive shocks of underground warfare.
The central nave of the castle wall was sixty arm-lengths wide and eighty arm-lengths high, vaulted with massive stone ribbed arches of dense black dolerite. Supporting the huge weight of the ocean above were twenty-four massive eight-sided piers, each eight arm-lengths thick, bound at intervals of four spans with heavy hoops of banded cast iron. The iron was crusted with a dry, stable patina of black magnetic iron, untouched by the acid-burning rot of standing salt water.
Qiao Ming stepped across the bronze threshold, his bare horn-hard feet gripping the dry, chiseled stone floor flags. The air in this stronghold was cool, dense, and clean, kept in constant breath flow by a network of upright air-flow chimney pipes that tapped the high heat drafts of the magma chambers. Across the stone flags ran eight curved drainage chimney pipes, each three spans wide, designed to direct any sudden intrusion of seawater into the deep drain pits below.
