Well the beach is always good, lol. You could hit Belmont Park, which is a couple amusement rides on the boardwalk down there. I really think everyone should walk around Balboa Park, though. It's gorgeous, lots of trees and grass (bring a frisbee and
I'm impressed with the new Spartan maps. They posted the one for the SOCAL races to Facebook, they now have elevation and make it more clear where things are.
Even better, though, is the Rock N' Roll DC. They added a youtube walkthrough of the whole marathon and half-marathon courses, with an elevation guide at the top. I don't think they did this last year, it's pretty neat.