The Steel Mace Barbarian Squat is one of those awesome exercises that works multiple movement patterns and muscles at the same time.
Like all squats, it's great for building strong and toned legs. But this squat variation also challenges the core and the arms as well. It's particularly good for the grip which is useful if you're a martial artist, or other athlete.
If you don't have a mace handy, you can use a cheap sledgehammer to similar effect.