Core Readings:
Ruins of Desert Cathay – Vol I, Chapter XXII, “To Keriya and the Niya River,” pp. 258 to 279 https://archive.org/details/ruinsofdesertcat01stei/page/258
Niya Ruins– Wikipedia 2 pages https://en.m.wikipedia.org/wiki/Niya_ruins
Recommended but not Required:
The Lost Kingdom of Niya, By Li Xiguang, Washington Post 7 pages https://www.washingtonpost.com/archive/1995/10/11/the-lost-kingdom-of-niya/61b54ad0-59fa-4a30-9f8d-5f38863eae07/?noredirect=on&utm_term=.e1542801885b