A 17th-century citadel called Kastellet houses part of the Defence Museum, south of the town centre. There are extensive displays of guns, blades, bombs and military uniforms, but the historical context they are given is somewhat scant. Some brief explanatory notes in English are available from the ticket desk. There are especially large displays on the Nazi occupation of the island and on the bombing of Rønne and Nexø by the Soviets at the end of WWII.