Subterranean Breach

I slipped sideways through the central aperture of the cast-iron grate, guiding both segmented mechanical appendages through the iron bars. A measured descent along the waxed cord brought my boots down onto the cool, galvanized floor of the duct. The acoustics inside are deep and cavernous. Ten inches ahead along the zinc tunnel, a sheet-metal air damper stood propped at a slight incline, held by a small slotted screw. I anchored my golden pick into a folded seam to brace against the warm updraft, then tapped the metal baffle with my right claw. A clear, resonant clang traveled far into the bends ahead. The subterranean corridor is open.