Venus de Miles, Boulder

Based in Colorado and Illinois, Venus de Miles is much more than the bike rides (30 miles or longer) and 5K runs—just for women—that it organizes. But those events aren't too shabby. They have drawn more than 12,000 participants, sending women of all fitness levels on empowering treks by wheel or by sneakers.

The reason for the all the pedaling and pavement-pounding? For one, it's a chance to get active women together in the spirit of sisterhood. For another, the events raise money for Greenhouse Scholars, a program designed to identify outstanding students from low-income communities and nurture these future leaders throughout their college careers.