Whether you're looking for fitness pals or people to hike or paddle with, Meetup.com has a lot of options. There are groups for runners and groups for walkers looking to get moving at an accessible pace. There's a paddling group and a weekly paddleboard meetup and a couple of meetups for rock climbers (or people wanting to become rock climbers).
Holly, a yoga instructor based in Orono, is the founder of Maine Yoga Adventures, an event company that combines yoga with an array of other fun activities, from hiking and tennis to writing and wine tasting.
I've been a big fan of the Meetup.com concept. I'm an even bigger fan since joining the Let's Go Do Stuff Meetup for a leisurely paddle on the Pleasant River and some impromptu rope swinging a few weeks ago.