Miyashita Park is an excellent use of urban space, allowing outdoor recreational activities in the middle of the city. It's a recreational sports park that is located five minutes' walk from Shibuya Station on Meiji Dori. Set amidst the high rise buildings it has an interesting way of making you feel both a part of the city as well as removed from it. The facilities at Miyashita Park include two football arenas, an area with rock climbing walls and a skatepark.
Update: The park underwent renewal and reopened on July 28th, 2020.
Find out more about Miyashita Park.