I'm curious, what do you guys do during the winter when the footing is too bad to ride?

I board my horse at a place that is built near marshland and therefore it gets very muddy and wet this time of year. There isn't really any good riding ground that is fit for anything besides walking or a careful trot. For more context, I have very limited access to an indoor arena and my horse isn't able to be turned out.

Therefore, I would love to hear some suggestions for activities that I could do with my horse that will keep him from getting too fresh and keep me engaged as well.