I tried winter swimming... the winter before last. I was never a great swimmer. Getting older didn't improve my swimming skills. I found the process of driving to the [swimming] center, checking in, changing, showering, getting a lane position, swimming, showering, drying, changing and then driving back home to begin my day.... a little labor some for 20 minutes in the pool.
Maybe if I was a better swimmer it would have been more fun or seemed like more of a benefit. I was surprised and disappointed when swimming didn't work out for me.
I don't bicycle for exercise. I bicycle because I love cycling. I have yet to find a cycling replacement... for any season. But I continue try different off-season exercises in hopes to find another sport as a fill-in for cycling. Last year I tried jogging... or jog/walking. I enjoyed that and still do a bit of that even in warm weather. It felt really great to get to a place where I can run... effortlessly.
This year/winter/off-season I bought a mountain bike and will be trying winter bicycling. I might give yoga class a try this winter as well. The main thing is TRY ANYTHING... and everything. Keep active, and keep being active, interesting.