Fort Denison is an island in Sydney Harbour, and has long been somewhere I have wanted to visit. When my family moved to Sydney it was something to look at and imagine ghost stories about - it is only relatively recently that plebs like us have been allowed to visit. We didn't get there last year, so I guess we have to write it on our list. My father and brother have been so I feel I am missing out. (To be honest, I didn't even investigate visiting because I didnt think it was possible.)
The fortress features a Martello tower, the only one ever built in Australia and the last one constructed in the British Empire. It is built from sandstone and the walls are between 3.3–6.7 metres (11–22 ft) thick at the base and 2.7 metres (8 ft 10 in) thick at the top, but the fort was obsolete by the time it was completed. The tower had quarters for a garrison of 24 soldiers and one officer.
Before the tower was built the island was known as Pinchgut and served as a prison (and as the town gibbet) but as far as I can tell only one person was ever sent there. These days there is a navigation light on top of the tower.