Calories burned: 8 per minute at a moderate pace, 14 at a high intensity.
The Work: Rowing has a history thousands of years old, with several different cultures having a different take on how to make it useful. Ancient Vikings and Mediterranean peoples may have been the most intense rowers, respectively constructing longships and triremes to make their way through icy oceans and fight in naval battles. Of course, rowers for those ships often worked under harsh, dirty, slave-like (if not slave) conditions to make the trips as quick as possible. Today’s rowers do so under much more agreeable conditions, and they do it by choice—another plus.
Accessibility: Pretty strong, so long as you’ve got an appropriate body of water nearby and a boat to row. We realize those are some rough stipulations, but there are places to rent boats and people who love rowing all over, and it’s your choice as to how intense you want to be about it.