We saw people playing badminton, doing tai chi exercises, singing, dancing (both ballroom and traditional flag dances), using a huge brush to write Chinese characters on the sidewalk with water, playing in a chamber orchestra, juggling . . .
No wonder Beihai is the most popular park in Beijing! It's also one of the prettiest. In the spring, the trees blossom out and the park is awash in pink and white blooms. One summer I went to a fireworks display at night. In the winter, the lake freezes over, with people ice skating. In the summer, they rent boats and paddle/pedal around the lake.
Because it's just a short distance west of the Forbidden City, the park was a playground for China's imperial family. It remains a playground today -- for everyone, not just royalty.
The centerpiece of Beihai Park is the Tibetan-style White Dagoba Temple which sits on an island in the middle of the lake. It's a bit of a hike up steep stairs if you enter from the main entrance, but on a clear day the view at the top is worth it. I tell friends just go up the steps slowly, with frequent stops to catch your breath.
I write about Beihai Park in more detail in my books, Parents Guide to Beijing and DIY Beijing.
If you don't visit Beihai when you're in Beijing, you're missing out on a special attraction. Unfortunately, most organized tours don't stop there.