If you're curious about what your city's underground infrastructure looks like but are too chicken to climb down into a storm water tunnel or to lift a heavy metal grate and drop into a utility tunnel, you'll want to take a look at The Vanishing Point.
This site documents one man's explorations of our industrial infrastructure and landscape. Much of his travels are underground in sewer tunnels, but he also explores power generation plants and abandoned, dilapidated industrial buildings.
There are lots of eerie photographs in dark tunnels and shots of beautiful rusting metal tanks, beams and bolts (scroll to orange-ish photographs toward the bottom of the page). Don't be such a stranger to the structures beneath your feet that make your urban lifestyle possible, visit this site. At least you won't get caught trespassing.