Hornsund is a fjord on the western side of the southernmost tip of Spitsbergen island.
The fjord's mouth faces west to the Greenland Sea, and is 12 kilometres (7.5 mi) wide. The length is 30 kilometres (19 mi), the mean depth is 90 metres (300 ft), and the maximal depth is 260 metres (850 ft). Hornsund cuts different geological formations, from the Precambrian to the west to the upper Mesozoic to the east, and it is perpendicular to the main regional fractures of Spitsbergen.
The coastline of Hornsund is diversified, with a number of bays at the mouths of mountainous glacial valleys. Some of these bays have appeared as late as the beginning of the last century due to recession of glaciers.
A Polish research station has been operating there since 1957.