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. Urban explorers are secretive by nature...