Attention, hikers, mountain bikers, and nature lovers: Mark your calendars for September 24, National Public Lands Day. You’ll be joining more than 170,000 volunteers doing upkeep and improvements at more than 2,000 sites across the country – think of it as physical goodwill for all those trails you’ve slogged up in your hiking boots or bombed down on your mountain bike.

It’s as simple as locating a volunteer project in your area and signing up. If you want to make a mini volunteer-vacation out of it, stay the night (or the whole weekend) in a campground or at an on-site lodge (though expect popular spots like Yosemite National Park to fill up early). For your time, you’ll get a voucher to return for free.

Don’t forget your camera, either: Snap a few pics of volunteers volunteering, upload them and you’ll be in the running for some cool gear from REI, including backpacks, sleeping bags and tents. (And judging by the winning entries from last year’s Volunteer Photo Contest, you don’t need to be a highly skilled shutterbug.)

If you really want to get into the volunteering spirit – and rub elbows with some pretty big names in rock-climbing circles – check out the Yosemite Facelift. Held this year from September 21 to 25, Facelift is the annual volunteer effort to clean up debris after the busy summer season before the winter rainy season kicks in. A few hours’ volunteering gets you a ticket for daily raffles, and events are on tap every evening, including a film by renowned adventure photographer Josh Helling about search and rescue at Yosemite. (And yes, you can buy beer.)

September 24 also coincides with Fee Free Day at more than 100 national parks that normally charge admission. But if you’re going to spend time in the outdoors anyway, why not give back by volunteering a few hours?

See our Yosemite Travel Guide for more trip-planning information, then use our Travel Search price comparison tool to find the lowest rates on flights, hotels, packages, and more travel deals.