Joaquin Miller Park
You could try Joaquin Miller Community Center in Joaquin Miller Park. Sounds like a cool party!
It is located in Joaquin Miller Park with lots of hiking trails. The Community Center has plenty of parking, a big room, an outdoor deck and a view of the bay.
Archived Q&A and Reviews
Have you tried any of the trails in Joaquin Miller park, just down Skyline Blvd. from Roberts? We've been taking our toddler there since she was about 2 years (she'll be 3 soon) and we love it. The Sunset trail is nice and wide and level, and if you turn left onto Skyline from Joaquin Miller blvd, (so, going toward Roberts Park, but before you get there) you can park alongside the Sunset trailhead. There are also some lovely loops starting from the main entrance to the park which is on Sanborn (just off of Joaquin Miller blvd.). The city doesn't provide particularly good trail maps, but I've heard there are better ones to be had, though I couldn't tell you where to find them. We just love exploring without the use of maps. Love our Oakland Parks
We take our 2.5 yo and 5 yo hiking around Montclair quite a bit. The Big Trees and Sunset Loop trails in Joaquin Miller Park are of our favs.
Sequoia-Bayview trail in Joaquin Miller Park -- take Highway 13 to Joaquin Miller Rd, turn left onto Skyline and after the first big bend in the road, look for the trailhead -- you should see cars parked near it. A popular trail for joggers, jog strollers, and people walking their dogs.