Fort Denison

This small fortified island sits in the middle of Sydney Harbour, a short ferry ride from Circular Quay. Once a rocky outcrop used to isolate convicts, it was built up in the 1850s with a Martello tower and gun battery amid fears of foreign attack, making it one of the last such towers constructed in the British Empire. A time-ball and tide gauge on the island have recorded harbour conditions for generations. Visitors reach it by boat to explore the tower, the barracks and the cannon.