Literally "Moon Garden" in Old Chinese. Partially subterranean city located on Earth's moon (Luna). Established by the Syndicate of Chinese Provinces in 161 AT (2130 c.e.) as a scientific research station (primarily in low-G agrisplice-culture, bionanotech, and hydroponics), it created quite a controversy when the Syndicate closed it to all but Chinese citizens.
Later it converted to a low-G recreation and rehabilitation facility and the ban was lifted. The city survived the Technocalypse thanks to an efficient blue goo defence network. The Treaty Org made a special target of Yueyuan during the Moon Wars, despite the fact that Yueyuan had welcomed many refugees after the Great Expulsion.
Now mainly a quaint historical locale (especially the Old City, a popular tourist jaunt).