The W&OD Trail is a 45-mile long paved trail for walking, running and bicycling which runs from Purcellville in Loudoun County to Shirlington in Arlington County. The park also includes an adjacent bridle path for horseback riding which runs 33 miles from Vienna in Fairfax County to Purcellville. Built on the roadbed of the former Washington & Old Dominion Railroad, the multi-use W&OD Trail traverses the urban heartland and countryside of Northern Virginia.