Gunpowder Falls State Park
Distance from DC: 1.15-hour drive
Located in Baltimore and Harford County, Gunpowder Falls is the largest state park in Maryland, so for natives, it’s not exactly a hidden gem. But then, nobody from DC is from here, so plenty of you probably haven't heard of it. And that’s a shame, because the 15,000-acre state park offers no end of great hiking trails. Go to the Hereford Area and enjoy any of its 21mi of hiking trails; when you’re done, try hopping into the Big Gunpowder River to cool off. The water is cold year-round, but in the summer after miles of hiking, it’s totally worth it.