Christianso is the largest island in the group of islands and rocks lying 18km to the east of Bornholm in the Baltic Sea. There are two inhabited islands, Christianso and Fredrickso and in 2019 there were 84 permanent residents between these two islands. There is a third island, Graesholm, designated a nature reserve and many rocky islets surrounding the three islands. The harbour is bisected by a swing bridge which connects Christianso to Fredrickso. There are two castles and the harbour is surrounded by a defensive curtain wall with a series of bastions and the islands were occupied solely by the Danish Military forces until the 1860s. The islands are managed by the Danish Army but most of the islanders today cater for tourists and there is a daily ferry to Bornholm.