Probably the coolest thing on our “tunnel tour” was learning about “prism glass.”
Prism glass is a type of building glass used to redirect natural light into underground rooms like basements and “areaways.” In 1895 Frank Lloyd Wright designed and patented 41 different designs.
In the picture above my buddy Louis shines a light from his iPhone through a piece of prism glass (held by tour guide John Atkins), while our friend Vicky looks on intently.
Below are photos of prism glass encased in a sidewalk. John “moved heaven and earth” and we were given access to a basement area directly beneath a prism glass sidewalk grid so we could see for ourselves how the natural lighting system really works.
Prism glass sidewalk grid (street view)
Prism glass sidewalk grid (basement view)
Prism glass sidewalk grid (basement view)