What is "grundkallen"

Grundkallen is a Swedish lighthouse on a shallow of the same name in the southern part of the Gulf of Bothnia, some northeast of Öregrund. The current lighthouse was built in 1961 to replace a lightship in the same location. It is a round concrete tower with a helipad on top and a round two-storey crew quarters in the bottom, both painted red, mounted on a round caisson which is painted black. The lighthouse, owned by the Swedish Maritime Administration, is automated and unmanned.