It's like a hiking trail, well it is a hiking trail during the day. So it is rocky, there are trees everywhere and it is really steep and hilly.
Update on directions: The hiking trail that was mentioned is not accessible by car. In general, it is the area behind Francis swimming pool (it's a huge outdoor public pool, so that is your best landmark) and it borders Rock Creek Parkway on the east between
P and M Streets (look at a map of the area just west of Dupont Circle and
all should become clear). It is a steep downgrade, at the bottom of which
is a creek. Paths snake through from end to end & top to bottom.
Crowd: All types
Neighbourhood: across from area # 6