Indoor (and outdoor) rock climbing is hands down the best workout I have ever had.
I used to go to the climbing gym for hours every day, and not only was I in the best shape of my life, but I could also eat anything I wanted and never gain a pound. It truly was the best hobby I've ever had. Looking forward to getting back into it. (Obviously, it is great for super rainy days in the spring, summer, and fall as well!)