I tend to mix the Biking with a bit of Hiking in Winter, as cold weather seems much less of an issue with Hiking as it does with Mountain Biking.
To make it interesting, I will Hike trails that I don’t bike on, otherwise it’s boring as hell (like seeing the same old stuff but in slow motion and with no chance of crashing!). Plus there’s some great trails that are only accessible by foot, with much more techy terrain.
Combine this with a few mountain biking trips abroad and there’s probably enough to keep things interesting through Winter. It must be said I still get more than sick of it by the end of it though and more than glad when its over.
I don’t bother with turbo training, zwift, street running, road biking, etc which I’ve seen a lot of mountain bikers start doing when Winter comes.