- Washington Park is a public park in Seattle, Washington, United States, most of which is taken up by the Washington Park Arboretum, a joint project of the University of Washington, the Seattle Parks and Recreation, and the nonprofit Arboretum Foundation. Washington Park also includes a playfield and the Seattle Japanese Garden in its southwest corner. To the north is Union Bay; to the west are Montlake and Madison Valley; to the south is the Washington Park neighborhood; and to the east is the Broadmoor Golf Club.