Martello tower built in 1686-1690. The top floor (cannon deck) houses a range of artillery. The lower floors have exhibitions of the history of Fladstrand and the harbor. Citadel Fladstr. was used as a base by the Danish Navy during the Great Northern War (1709–20) and the war against GB (1807–14). Tordenskioldsdage is a historic festival that with a spectacular staging of the Powder Tower brings the audience back to the year 1717.