Just tried mountain biking today for the first time. It was great. My son lent me his old Specialized Hardrock and took me to a greenbelt area right on the edge of our neighborhood. It's pretty flat around here, but this tiny area had lots of varied terrain: wide, smooth paths through a mature pine plantation, boardwalks over marshland, smoothly eroded rock hills, and narrow, rooty, rocky paths. What with all the braking, accelerating, climbing and descending, it was a pretty good workout. The scenery was nice, and the place was crawling with smart deer taking advantage of the no-hunting rules. Fun stuff.