Yarkand

Yarkand was located on the western side of Cathay. The First Doctor, Susan, Barbara, and Ian travelled through Yarkand with Marco Polo, while moving from the Plain of Pamir to the town of Lop. (TV: "The Roof of the World")

Behind the scenes
Yarkand is never seen in the story itself, as Marco Polo's narration skips over the journey from the Plain of Pamir to Lop. This narration, however, describes the journey through Yarkand in scarce detail.