The guano-covered Gardner Pinnacles (Hawaiian: Pūhāhonu) are two barren rock outcrops surrounded by a vast reef and located in the Northwestern Hawaiian Islands (about 950 km or 590 mi northwest of Honolulu). The total area of the two small islets – the remnants of an ancient volcano that is the world’s largest shield volcano – is only about 24,000 sq m (5.9 acres). The highest peak is 52 m (170 ft). The expansive, surrounding reef, however, has an area in excess of 1,900 sq km (735 sq mi). Photo courtesy of NOAA / Andy Collins.