Ouyi is situated in Nushabad city, Isfahan province; 3 km west of Aran and Bidgol. Ouyi; the Underground City area is 4 km2 and with national registration number, 15816. Nushabad city has 31 hectares historical area, which the underground city of Ouyi; the world’s biggest underground city is one of them. This city has history of 1500 years.