Two feet beneath the grass of Tercentenary Theater, maintenance workers check pipes and pressure gauges in perfect quiet as the voices and heat of the University rush overhead.

Under Mill Street outside Winthrop House, two carts pulling trailers full of salad, soup and uncooked lasagna pass each other with the whirr of electric motors.

At the core of the Weeks footbridge in a three-foot crawlspace, three steam pipes make the temperature close to 100 degrees for workers crawling through to the Business School.

Just underneath the sidewalks, classrooms and bedrooms of the University is a system of walkable passageways, bringing light, heat, communications and sometimes food as far north as the Law School and as far south as Peabody Terrace.

Welcome to a world of utility and rumor. Welcome to the tunnels-Harvard's underground.

Steam Tunnels

The University relies on centrally distributed steam to heat the majority of its buildings. The steam that heats every room in the river Houses and the Yard starts out two blocks past Peabody Terrace, in a plant run by the city of Cambridge.

An existing network of steam tunnels was extended to this site in the early '20s, with an extension to the Business School-disguised at the hollow center of the Weeks Bridge-laid in 1926.

In their current form, the tunnels leave the steam plant, pass in front of Mather and Dunster houses in the Memorial Drive sidewalk and then head under Old Leverett to Mill Street.

From Mill Street, tunnel spurs take steam, power, telephone and data lines to the other houses along the river, but the main line runs under Lowell House and up under Linden Street to the Yard.

After shrinking to another crawlspace as it passes over the Red Line under Mass. Ave., the tunnel branches under Wiggles worth Hall, with spurs and impassable buried lines covering all the Yard buildings.

North of the Cambridge Street overpass, where it is again impassable, the tunnel then links the Science Center with the Law School, Divinity School and Biological Labs. In all, there are 3.5 miles of walkable tunnels beneath campus.

The tunnels vary in size, but most are about eight feet square, with 12- and 10-inch steam pipes along each wall-their 380 degree-plus surface temperatures dulled by four inches of insulation. Inside steam rushes by at 100 pounds of pressure. Overhead are the black cables that bring the University power and communications ("We don't have telephone poles," says Secretary of the Faculty John B. Fox Jr. '59), and underfoot is brown residue from shallow pools of groundwater.

"It's a pretty unglamorous place," says Michael N. Lichten, director of the Office of Physical Resources in the Faculty of Arts and Sciences (FAS). "In some ways it's like going into a mine."

During the winter, when each of the three steam pipes hits 430 degrees, the temperature in some parts of the tunnels can climb past 100 degrees.