Leaving the roofless survey hut behind them in the center of the Trapped Court, the four companions walked toward the northern boundary of the enclosure.
Here, sixty paces north of the breached window where they had entered, the limestone cliff formed a wide, natural nook sheltered beneath a huge rock overhang that projected twenty feet out over the courtyard. Nestled deep inside this protected recess was the stone-built heart of the Old Kingdom mountain station: the main portal of the original map room.
It was an amazing, round-headed stone archway twelve feet wide and fourteen feet high, built of massive, rusticated blocks of dove-grey limestone. This portal was the entrance to the main underground archive vault that had remained behind in the parent rock. Just then, the front half of the station—including its eight-sided watching tower—had been swapped across Needle Gorge a century earlier.
Yet the archway offered no open passage.
From the keystone of the arch down to the massive limestone threshold doorstep, the entire opening was sealed by a huge, ribbed counterweighted iron fire-shutter.
The shutter was forged from heavy, corrugate-rolled wrought-iron plates two inches thick, heavy with level T-section ribs riveted across its outside face at one-foot intervals. The upright edges of the plate sat deep inside two heavy, cast-bronze guide tracks embedded three inches into the flanking limestone stone support pillars. The entire surface of the iron was coated with a dark, waxy dressing of black pitch and graphite grease. It had preserved the metal against…
