Are there any martial arts, or hobbies that are good exercise, that I can learn at home?

I am going to be spending about 3 months in a fairly isolated rural location. I am going to need to fill the time somehow. As I work as an illustrator I can spend a lot of my time sat still, so I need something that gets me off my butt!
I already run and walk but the weather at this time of year often prohibits that. It would be preferable to do something that doesn’t require a lot of expensive equipment but I cant really think of anything. Does anyone know of any fun and energetic hobbies that can be done around the home or big indoor spaces?

Any Ideas gratefully received.