I've had the two-ton steel Trek Antelope 820 "Frigid Rigid" for a couple of years now as a cruiser/beater but never got round to playing in the dirt. Finally took it on the easy two-track "green" trails at Stoney Creek park this past weekend. Fun! Hills got the heart rate up and who knows - if I do it a couple of times a week and try some more difficult trails it might make me a better road hill climber too.
Heavy and entry-level as the bike is, I still like the handling. The first homemade MTBs were made from heavy steel cruiser frames, yes?
So there - another dimension to my biking.