The closest subway stop is Columbia Heights (Green and Yellow lines). Exit the station on the West side of 14th Street. (If you take the escalator out of the station you will come up facing West.) Walk 1 block West on Irving Street (long block) to 16th Street. Turn left on 16th Street and walk 5 blocks South on 16th Street. The park will be on your left.
You can also catch a bus. The S2 & S4 buses run between the Silver Spring Metro station and downtown DC on 16th Street. For the bus schedule/map click here.
From downtown DC (National Mall):
Go north on 14th, St., turn left onto M St. go two blocks and turn right onto 16th St. At W St. turn right, go one block and turn left onto 15th St. There is a small of street parking lot on the left of 15th.
Take 16th St. south to W St. and turn left, go one block and turn left onto 15th St. There is a small of street parking lot on the left of 15th.