Bornholms Forsvarsmuseum is Rønne's defence museum, set inside Kastellet, a round citadel tower built in 1744. The fort was never used in battle, but its thick walls make a fitting setting for the island's military-history collection.
The museum displays weapons, uniforms, blades, bombs, and other artefacts from Bornholm's defence history. It is a good add-on to Rønne's old town and Bornholm Museum if you want a fuller picture of the island's past.