Heligoland (German: Helgoland; Heligolandic: deät Lun ["the Land"]) is a small German archipelago in the North Sea. Formerly Danish and British possessions, the islands (population 1,127) are located in the Heligoland Bight (part of the German Bight) in the south-eastern corner of the North Sea. They are the only German islands not in the immediate vicinity of the mainland and are approximately three hours' sailing time from Cuxhaven at the mouth of the River Elbe. In addition to German, the local population, who are ethnic Frisians, speak the Heligolandic dialect of the North Frisian language called Halunder. Heligoland was formerly called Heyligeland, or "holy land", possibly due to the island's long association with the god Forseti.Heligoland is located 46 kilometres (29 mi) off the German coastline and consists of two islands: the populated triangular 1 km2 (0.4 sq mi) main island (Hauptinsel) to the west, and the Düne ("dune," Heligolandic: de Halem) to the east. The former is what the place name "Heligoland" normally is used to refer to. Düne is somewhat smaller at 0.7 km2 (0.27 sq mi), lower, and surrounded by sand beaches. It is not permanently inhabited, but is today the location of Heligoland's airstrip. The main island is commonly divided into the Unterland ("Lower Land," Heligolandic: deät Deelerlun) at sea level (to the right on the photograph, where the harbour is located), the Oberland ("Upper Land," Heligolandic: deät Boperlun) consisting of the plateau visible in the photographs and the Mittelland ("Middle Land") between them on one side of the island. The Mittelland came into being in 1947 as a result of explosions detonated by the British Royal Navy (the so-called "Big Bang"; see below). The main island also features small beaches in the north and the south and drops to the sea 50 metres (160 ft) high in the north, west and southwest. In the latter, the ground continues to drop underwater to a depth of 56 metres (184 ft) below sea level. Northwest of the island proper Heligoland's famous landmark is found: the Lange Anna ("Long Anna" or "Tall Anna") is a free standing rock column (or stack), 47 metres (154 ft) high. The two islands were connected until 1720, when the natural connection was destroyed by a storm flood. The highest point is on the main island, reaching 61 metres (200 ft) above sea level. Although culturally closer to North Frisia in the German district of Nordfriesland, the two islands are part of the district of Pinneberg in the state of Schleswig-Holstein. The main island has a good harbour and is frequented mostly by sailing yachts.