Until 1961 Grönskär was the approach beacon for Sandhamn, when the beacon Revengegrundet took over. The beacon at Grönskär had guided seafarers since the 18th century. Grönskär is a flat island E of Sandhamn and is known as the place for the beacon. The Grönskär beacon was built in 1770 by granit and sandstone. It was then an open coal beacon. In 1910 it was converted to a conventional electric beacon. Three families lived permanently on Grönskär in order to operate the beacon. From time to time they had many children. One reason was that government was obliged to run a school and supply a teacher, if the site had more than three chidren! Skärgårdsstiftelsen now owns the land in the old village, Norra hamnen and the old beacon itself. Parts of Grönskär is a nature reserve.