On the first day of UC Irvine English professor Carol Burke's Introduction to Folklore course, she asks students to write down any unusual stories they've heard about their campus.
Someone always mentions the tunnels.
Rumored to have been built as escape routes for professors and as access points for National Guardsmen during student protests in the 1960s, the 1 1/4 -mile concrete corridor runs in a circle below the campus' original buildings, connecting to building basements and vaults.
School officials say they don't know where the rumors started; the passageways were built in 1964, well before most student demonstrations, and they house only heating and cooling pipes.
Because of security concerns, UC Irvine and other universities across the country are sealing off tunnels that have drawn curious students and urban explorers, played host to hazing rituals and pranks and sparked urban legends, such as the one about mutant radioactive rabbits.
UCLA has blocked off areas of its 6-mile tunnel system. Columbia University is securing its tunnel entry points with new doors, locks and card readers. Stanford, which used to count tunnel exploration as a campus tradition, recently invested in chains, padlocks and gates to keep students out of its 10-mile system after officials discovered that some of them had ventured under the main quadrangle -- alarmingly close to the president's office.
UC Irvine is the latest to install a sophisticated security system for its tunnels. The university is spending up to $300,000 on motion sensors, alarms, closed-circuit cameras and card readers to replace the old locked gates that weren't entirely successful in keeping students out, said UCI Chief of Police Paul Henisey.
"There's a lot of people on campus who have no idea where these tunnels are or how to get into them," said Paul Howland, director of plant operations. "We want to keep it that way."
Since 9/11, universities have been looking for anything that could make them vulnerable to terrorism, said Lisa Sprague, president-elect of the International Assn. of Campus Law Enforcement Administrators.
"Steam tunnels have come to the attention of universities just because of their safety hazard and their enticement to students and others to be adventurous," she said.
Ada Meloy, general counsel for the American Council on Education, said bouts of school violence such as the Virginia Tech shootings "have made colleges and universities once again focus on how vulnerable the buildings and campus are to a person seeking to create havoc."
Even without the threat of terrorism, campus officials call the passageways an "attractive nuisance," an intriguing part of the campus landscape that is a liability to schools if not locked and monitored.
Some colleges, such as the University of Michigan and the University of Washington, said their tunnels have been secured in recent years but would not provide details. Others, such as Princeton and Caltech, were so concerned about tunnel details falling into the wrong hands that they would not comment for this article.
Utility tunnels are common at large building complexes that share a central heating and cooling plant. The passageways serve as a distribution system for water and steam that regulate the temperature of buildings, as well as fiber optics and other wiring.
They serve as the subterranean arteries for civic centers, medical facilities and many colleges and universities, giving workers easy access to repair aging pipes and wires.
"Without this, we would have to dig big holes in the campus every time we had to work on a pipe," UCI's Howland said on an increasingly rare tunnel tour.
Despite their utilitarian role, the tunnels for decades have spawned urban legends and conspiracy theories among students.
"They didn't want another Berkeley," said Joel Montano, a fourth-year sociology major at UCI, recounting the prevailing theory that the tunnels were built for riot control.
At Johns Hopkins University, a rumor circulated in the mid-'90s that mutant rabbits from an underground nuclear experiment lived in tunnels below a physics building there.
Burke, the English professor and folklorist, calls the fascination with entering the tunnels an example of "legend tripping," an age-old practice in which a group of young people investigate a storied place for themselves.
"The subterranean world is really handy to make the site of legendary happenings," she said. Because of their hidden nature, tunnels have at nearly every university developed a distinct mythology, she said.
At the U.S. Naval Academy in Annapolis, Md., she said, students call their campus tunnels the Ho Chi Minh Trail and say they have used them to haze first-year midshipmen.