Riding a bicycle. I find cycling very satisfying for all sorts of reasons, and although it can seem easy to compromise on cycling (infrastructure isn't there, car is easier, whatever) it's a joy when it's happening.
Follow-up to that. If you go into cycling do not bother about equipment, but about the cycling.
I rode a bike that I rescued from the dump for over a year. Besides a new chain, tubes and loving maintenance it was a nice solid 70s era bike. I swear it was made out of iron pipe. Oddly, it came with track drop bars.