FULL STORY: http://www.startribune.com/stories/462/5620554.html Use http://www.bugmenot.com for a username / password if prompted to register He calls himself Max Action and, as much as possible, he tries to live up to the name. He says he has climbed to the top of the Washington Avenue Bridge in Minneapolis, walked in underground rivers, wandered through abandoned mental hospitals and cartwheeled naked on the stage at Northrup Auditorium at the University of Minnesota. All in the name of urban exploration, an apparently growing -- and illegal -- subculture in the Twin Cities and around the country in which people break into and wander around forbidden or foreboding places in their cities. "It's just one of the most enjoyable things I've found to do," said Action, a 28-year-old Minneapolis resident who studied philosophy at the University of Minnesota. He spoke about the pastime on the condition that only the pseudonym he uses among similar explorers be used, not his real name. Urban explorers are secretive by nature and at times commit criminal acts, so it's hard to estimate how many are around. But the number of them exploring caves, factories, storm drains, munitions plants, breweries, underground rivers and other places appears to be increasing. "The underground is getting terribly crowded," said Greg Brick, 42, who calls himself the grandfather of the scores of urban explorers in the Twin Cities. "Everybody and their brother is doing it, and drawing a lot of attention to themselves." Just last week, St. Paul police arrested three college students for breaking in to the city sewer system near City Hall. The trio, carrying gunpowder and fireworks, said they belong to a group called Urban Invaders. Two years ago, when the country was at a state of heightened alert, a group of six urban explorers were arrested near the Gopher State ethanol plant in St. Paul. They carried night-vision goggles, two-way radios and other suspicious items. Charges were not filed in either case. But the incidents did draw the attention of authorities, who view urban exploration as a growing nuisance with a great potential for danger. "We do consider it a serious problem," said Pete Crum, spokesman for the St. Paul Police Department. "It is dangerous. There's always the danger of noxious gases when they go down there. They can cause damage, they put other people at risk, especially if they become trapped and we have to go in and get them." Several years ago a group of teenagers died from noxious fumes while exploring the Wabasha caves in St. Paul. Brick said carbon monoxide is but one of the many dangers facing urban explorers. There is loose asbestos, especially in the utility tunnels, as well as dangerous bacteria in the sewers. "There are places where there's so much loose asbestos it looks like snow," said Brick. "I wear a mask, but I'm sure 99 percent of the [newer] people ... just go down there breathing in asbestos." Urban explorers said the Twin Cities area, especially St. Paul, is considered one of the most appealing destinations in the world.