This is a parcel of land donated to the City of Boise, with the stipulation that is has to be a public park. That may take a while, because while the land is free, the rest of the "parkness" is not - landscaping, parking lots, play structures, sprinkler systems, signage. Right now, the fence is locked and there are "no trespassing" signs up. Boise has an extensive park system. See some examples here and here.