Huckenpahler's research paper on DC underground tunnels quoted above also contains this weirdly telling passage:

All electronics are forbidden. Anything that uses electricity and/or contains a chipset must be left at the door. Descend the stairs from street level. As you enter the main chamber, get fresh towels from an attendant. Proceed down the tunnel. Watch your step, as the only light source is low, bioluminescent blue-green laid into the trolley tracks. The baths line the walls on either side of the tunnel. Each is a minimal, white, marble rectangle with four- inch walls. Notice that many of the baths have soft green moss growing on their outer sides. The interior cavity is roughly a foot deep, four feet wide, and nine feet long. They are regularly refilled by attendants with cool spring water until the surface tension creates a faint pillow at the lip of the marble. Find an unoccupied bath. Remove your clothes and place them on the shelf at the head of the bath. Get into the bath, close your eyes, and turn off your mind. This is ruin porn. Everything is designed to degrade gracefully, including your body