If you're looking for a park then timberline, but you're going to have to do some research on places to hike if you want some actual good terrain. But honestly I've been all over the country and summertime in Oregon is the best anywhere, maybe except San Diego which has fine girlies everywhere and TJ if ur into donkey shows and cheap tequila. So take advantage of that and go surfing, mountain biking at hood, or hit up one of the many sick concrete skateparks in Portland or across the state.