West of the Forbidden City sits Beihai Park (beihai gongyuan) which was originally built for Kublai Khan before the Imperial Palace was even imagined. The scale of the park is appropriately regal and the huge lake is divided into three parts: Beihai (the North Lake), Zhonghai(the Central Lake) and Nanhai(the South Lake).
A walk around the various scenic spots in Beihai is definitely enjoyable. There are various places to take in along the way including: Jade Islet Isle, the Jade Jar of Dushan, the Painted gallery, the Nine Dragon Screen, the Liulige Tower, Yong'an Temple, the Five-Dragon Pavilion. There is also an expensive but classy restaurant "The Fangshan" where reportedly the Empress Cixi used to dine!
Beihai is a peaceful place to wander and do some people watching. In summer, some ignore the No-swimming signs and dive into the lakes. In winter, skating is a popular pursuit.