For southern Wisconsin, how about just getting out on cross-country skis? There haven't been many opportunities in central Illinois for some time, but quite a few of my bike friends would get together in the local parks for some laps. Definitely a good way to get outside for some exercise and you don't even have to clean up a bike afterwards! If you miss gluing on sew-ups, you can get skis that need to be waxed (I've got a pair).

For vintage indoor riding, I think rollers are the obvious choice. I don't think they are dangerous, but I learned to ride them back when I was young and healed quickly.

Steve in Peoria
(managed to ride 25 miles today before the storm arrives)