The yellow-tiled Id Kah Mosque, which dates from 1442, is the spiritual and physical heart of the city. Enormous (it's the largest mosque in Xinjiang), its courtyard and gardens can hold 20,000 people during the annual Qurban Baiyram (Eid). Non-Muslims may enter, but not during prayer time. Dress modestly, including a headscarf for women. Take off your shoes if entering carpeted areas and be discreet when taking photos.