Houhai Lake has beautiful running loop with lake views and traditional Beijing architecture. The full scenic perimeter route covers about 4km if you include the connecting paths between the three lakes (Houhai, Qianhai, and Xihai). Early morning 6-7 AM you'll share path with locals doing tai chi and morning exercises.

Mostly flat with good surface, some cobblestones near hutong entrances. Public restrooms and water fountains available. For a shorter option, just the main Houhai lake loop is about 2.8km if you stick to the direct waterfront path.

Best part is experiencing how Beijing residents start their day before tourist crowds arrive.