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, crawling across 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.
Today, tunnels may be enjoyed from aboveground during the winter months. When snow is on the ground, look for it to melt markedly faster in certain pathways a few feet wide, in certain predictable places every season. These are the strips of land above the imperfectly-insulated steam tunnels.