A fellow acquaintance of mine is really into a form of urban exploration called craning. It basically involves gaining access to, and climbing up onto active cranes. Some of the larger cranes in Toronto sit 30+ storeys up, and another four or so for the crane. You can see how it might take a bit of time (and stair climbing) to access some of these cranes.
Although it may sound dangerous, Wikipedia does not report any deaths from craning. I guess the big question is -- am I ballsy enough to do this? Time will tell.