Long time no see, everyone. I'm wondering if anyone knows of a high intensity martial art that can be learned solo. I was researching Capoiera, and while it could be learned without a partner, it wouldn't be very practical. I'm looking for something like yoga that can be mastered alone without compromising the integrity of the culture behind it. I'd prefer that it has the same intensity as running. It rains a lot here so I generally have to exercise indoors and I have limited space. Anyone know anything? Obviously there's straight up calisthenic exercises but I'm looking for something that can become a hobby.
To be honest there isn't much martial arts wise that would be relevant or useful (beyond being intensive exercise) without a partner. You could try and find a partner who wants to train with you in which case there are lots of options. If not then Shane's suggestion would probably be best. Don't dismiss calisthenics out of hand however, they can be approached as a hobby. I do exactly that because it is quite progressive and offers a decent sense of achievement. I've done a lot of martial arts in the past and at the moment I am unable to train with a partner I find calisthenics very satisfying.
Al Kavadlo's website (http://www.alkavadlo.com/) is probably the best I have come across. He ranks different exercises (http://www.alkavadlo.com/2010/05/14/mastering-your-body-weight/) so it is easy to get a sense of progression. Whatever you decide in the end consider throwing in some calisthenics and HIIT drills just to mix it up. Whatever you decide I would suggest keeping a small journal of some kind to keep you on track and to see improvement. Hope that is helpful.
No martial art can be learned solo, you need to find a good teacher, good sparring partners, and go from there.
An additional option for you might be prasara yoga
Hang a heavy bag/speed bag in your basement and go online to learn some combos. Not a martial art, but its a fun cardio workout and stress reliever and I consider learning the combos a hobby.