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...