Underneath the sidewalks and buildings so familiar to University of Wisconsin students lies a maze of terrain even the most seasoned campus veteran might not know about.

But for more than a century a labyrinth of tunnels, complete with encased piping, electrical wires and cobwebs, has supplied steam heat to most of the buildings on campus from heating stations on Charter Street and Walnut Street.

While campus engineers tout the steam tunnels' efficiency in distributing heat for a campus the size of UW, the subsurface inferno has not gone without its problems.

"It used to be a fairly routine occurrence for students to go on scavenger hunts down there," UW Police Assistant Chief Dale Burke said. "Or it was something kids would do after bar time on a weekend."

But it is not a good place for unauthorized people to be, he added. With high-voltage electrical wiring and low-hanging pipes transporting steamy hellfire, the dungeon houses as much risk as it does mystery.

"It's dangerous in the tunnels, especially in some of the older ones," UW physical plant director John Harrod said. "For people's own safety and overall campus security, we don't want anybody down there."

According to Harrod, university dollars — to the tune of nearly $100,000 — are being poured into the tunnels to prohibit unwanted guests.

The improvements to the steam tunnels came, at least in part, in response to recommendations from an "extensive survey" aiming to ensure campus security after the terrorist attacks of Sept. 11, 2001.

Not all of the work on the steam tunnels this year has been security related, however. One of the oldest tunnels on campus, snaking below Bascom Hill, was renovated this fall after its brick archway began to give way, Harrod said.

While some tunnels have been retired, functioning only as a reminder of UW's antiquated beginnings, miles of weaving tunnels still harbor steaming pipes — and sometimes underground travelers as well.

"We occasionally find blankets and sleeping bags down there," Burke said, adding that homeless people have been known to camp out in the tunnels.

The most illustrious tunnel roamer, "Tunnel Bob," has been around for campus for 40 years, Burke said, and has "made a living of patrolling the tunnels."

But a decade or so ago, Tunnel Bob suffered burns to his arm while inspecting equipment in the underground lair, Burke said, which goes to show how dangerous the maze can be.

"There's a guy who probably knew the area as well as the steamfitters, and even he got injured," Burke said. "It's not a place for people to go if they aren't authorized to be there."

Since the renovation of the tunnel's entrances, only university employees from the Facilities, Planning and Management Department, and campus police have access to the tunnels.

And according to Daniel Dudley, UW campus utilities engineer, any individual caught breaching the tunnels' security will be charged with trespassing.

"I don't want anybody hurt," Harrod said. "That's my biggest concern."