I bike commute every day, but it is only a short ride. So I've been going to the gym's spinning classes occasionally, about 1x to 2X week.

Instructors vary widely in their approach. Some lead a pure cardio class without much reference to real cycling (bouncing in and out of the saddle, doing push-ups on the bars, pedaling backwards, high cadence standing). Others are cyclists and lead a cyclist-oriented class (seated suffering, intervals, sprints). When necessary, I do my own thing and use the class for motivation and pacing.

I've used the classes to work on specific things, too. One is pushing high resistance, simulating big gears. Another is smoothing out my stroke at high cadence.

Overall I'm retaining more fitness this winter than I would be otherwise. Not falling on slick or icy roads. And the scenery in some of the classes is very fine. Practice your, err, drafting.