twin residential communities, southeastern Oahu island, Hawaii, U.S. Extending along Kailua Bay, they lie 13 miles (21 km) northeast of Honolulu and just south of Kaneohe. According to Hawaiian legend, the mountainous area surrounding Kailua was formed from a giant turned to stone. The communities occupy a superb white-sand beach where Oahu's ancient kings lived; the beach is now a popular recreational site, particularly for windsurfing and surfing. The Kawainui swamplands, to the west, were once royal fishponds. Many residents commute to Honolulu by the road tunnel through the Koolau Range. Offshore Popoia Island (Flat Island) is a state seabird sanctuary. Just west of Kailua is Ulupo Heiau State Monument, which preserves the ruins of an ancient Hawaiian religious site. Pop. (1990) Kailua, 36,818; (2000) Kailua, 36,513.