I shattered an ankle in a skydiving accident back in 1992. After 2 surgeries and over a year of therapy I eventually got to where I could walk pretty normal, but never got enough range of motion back to be able to run.
Over the years it's gotten a lot worse, and I even have trouble walking more than a half mile or so at a stretch, so any high impact stuff is out.
I did pick up a nice Trek mountain bike a couple years ago.
I travel for work, so if I'm going somewhere that has decent terrain and trails I take it with me and try to ride when I get a day off, but I'm usually pretty spent after 10 miles or so. Biking gets pretty hard on my old back too.
Around home there's not many places that don't have brutal hills, so I don't really enjoy the bike much at home.
I try to use the fitness rooms in the hotels, but the only things I can use comfortably are the recumbent bike and the elliptical. Neither of which are very exciting though.

It would help if I my wife would workout with me, but she doesn't really enjoy it either.

I guess I just have to make myself take the time to get started. (Getting old sucks) LOL