Done that with a few stadiums myself. Would imagine a place like the Rose Bowl is locked down fairly well, but it's a beautiful place. Another really cool stadium (with setting) I wandered into once was BYU's. That would be a really cool place to see a game. I was going to visit Colorado, Colorado State, and AFA's stadiums during a vacation in June but Chinaman eating a bat for lunch f'd that up. Maybe next summer...
LOL! I did the same at BYU. Just walked in.