Millennium Island - known as Caroline Island prior to 2000 - is located at the southern end of the Line Islands, which make up the western portion of Kiribati. Uninhabited Millennium Island is formed from a number of smaller islets built on coral reefs. The reefs grew around a now-submerged volcanic peak, leaving a ring of coral around an inner lagoon. The shallow lagoon waters are a lighter blue than the deeper surrounding ocean water; tan linear "fingers" within the lagoon are the tops of corals. The two largest islets are Nake Islet (on the north) and South Islet. Image courtesy of NASA.