Steam Tunnels connect all the major buildings on campus. They are used to transfer the steam from the heating plant to the buildings during the colder months. The steam tunnels are large enough for people to crawl through, and in earlier generations of Williams students, cross campus via the tunnels was a popular pasttime.
This ended, reportedly, when a student fled Security through the steam tunnels and seriously injured himself in his haste, needing to be hospitalized. Since then, tunnels are very sensitively alarmed and locked tightly, although a few openings may still exist.
The Facilities description of the tunnels can be found here: Steam Distribution System
