I've never been interested in sport of any kind, whether watching or participating. But I used to go swimming for a few hours a day, six days a week when I was a kid. I'd swim now, but without your own pool, it's a right-old hassle.
I also love riding my mountain bike. I've managed to fit a rack and panniers, and I don't drive any more, so it's my main mode of transport. And, if I don't need to go anywhere, I just ride around for 10 or 20 miles.
I can't explain why cycling feels like so much fun. There's the peace-and-quiet, the fresh air and countryside, the feeling of freedom, the air rushing through your hair...
I have a friend who ditched her car and got around by bike for a number of years. She was in killer shape and never even realized it until we talked her into some races. Commuter miles sneak up on you. If you were to keep track, I bet it would be a pretty big number at the end of the year.