Tickets for Beijing happy valley

Hi i am going to beijing happy valley next week. I'm just wondering if you know any websites that sell tickets to it? Also any tips in general for being in china or hong kong?

^It's been quite a few years since we visited that park. We would hire a guide to buy our tickets before hand so we were ready to go.

As for tips for being in China, perhaps go through some of our old trip reports. Very different culture, especially at the parks.