In the 1830s the British built five 'Martello' towers – copies of the tower at Mortella Point in Corsica (vowel order was apparently not a priority for the British) – to protect their young colony from predators (namely the French, who were suspected of supporting a slave rebellion). The one at La Preneuse is now a small museum where captions explain the tower's ingenious design – 3m-thick walls are crowned by a copper cannon that could apparently destroy a target 2km away.
Entry includes a guided tour and there's a small shop.