Steam tunnels are the things that run under universities and have steam pipes and light bulbs in them. At my university, the tunnels were covered with 1/2" thick steel plates that took four people with crow bars to remove. The best time to break into the steam tunnels is from 3-5 am, especially while it's raining, since this reduces the possibility of passers-by. Be sure to have a getaway car and a spotter or two. Be careful, you might get into trouble if you're caught. I wasn't. The police will consider you a thief, or at least charge you with breaking and entering, if they get you.
The whole point of doint this is to have fun, which is something that some people like mundanes, normals, induhviduals, fundamentalists, and prudes don't understand.