This lovely tea house is hidden away inside Tiānxīn Park, down the path from the entrance to the Old City Wall and Tiānxīn Pavilion. The building actually straddles part of the ancient wall, and you can sit beside it on the tree-shaded terrace. It can be smoky.
The tea menu is in Chinese, although each tea category – green, black, oolong – is written in English, so you at least know what type of tea you're ordering. Some teas are priced per cup (杯; bēi), others per pot (壶; hú). As always, you can fill up your cup or pot with hot water as often as you like.