The Oakland zoo is a wonderful place. I just recently went there to spend some time with my girlfriend. I went there thinking that it would be an ok experience, just because we are in our 20s and no longer kids. But I was shocked at how interesting and amazing the zoo is. Seeing monkeys, exotic birds, and bears is truely a fascinating experience, even for grown ups. The prices aren't bad, it's cheaper than the SF zoo. Another plus about the zoo is it's location, after going to the zoo you can play a round of golf because a golf course is next door!
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