What do you do, to keep the fitness up?

I don't do indoor training; I'd rather gear up and deal with it. But 35-40F, rain, and dark, which describes much of the winter here in the PNW, it's hard to find motivation for anything over an hour. It's already getting dark at 5pm.

I've got an R-12 going, which means I'll manage to squeeze a 200 km ride in once a month, hopefully on the best weekend. I have the lights and the gear. But I can do a 200k per month and still lose plenty of fitness. That 200k can turn into a 13 hour slog if I don't do some training in-between.

The question is, if you've managed to stay fit with riding outdoors through a non-Florida winter, what have you done?