Sunrise at Rock Creek Park (©James Losey, Flickr)
One of the country's earliest, urban national parks, this 2,000-acre wooded oasis follows its namesake waterway through the heart of the city. Shady paved trails draw bikers, joggers and skaters. On weekends and holidays, portions of Beach Drive close to motorized vehicles. Also tennis courts, a golf course, stables and a planetarium/nature center (Wed.-Sun. 9 a.m.-5 p.m.) with ranger-led tours. Free (fees for some activities).