DC was built on a marsh, a beautiful, brackish, low-lying ripple of saw grass and steel-blue water, wind-coaxed and tide touched by the inflow of the Potomac from Chesapeake Bay. You’d never know all that now, of course, unless you come to the USA's only national park devoted to water plants. See the natural wetlands the District sprang from; look out for beaver dams, clouds of birds and the more traditional manicured grounds, quilted in water lilies and lotus.
The gardens are a lovely refuge, and you'll likely have them to yourself. A cool boardwalk juts out into the water at the park's southwest edge. The Anacostia River Trail starts from near the visitor center. Kenilworth is about a mile walk from the Metro.