Today marks the 19th annual event sponsored by The American Hiking Society.
Maryland, D.C. and Virginia residents are celebrating with a variety of outdoor activities, including a bird watching walk, a garden tour and a scavenger hunt.
Beth Mullin, the executive director of Rock Creek Conservancy, says while she wants to do it all, she'll end up at the Mindfulness Walk - a quiet, mindful trek through the park.
"It's a wonderful way to exercise, and to be in the woods, and to find out to find about the rich natural heritage we have right here," says Mullin.
Last year's Trails Day brought in over 300,000 participants nationwide.