Fort Denison.
Named after an early Governor the Fort is a Martello design built on a low lying island called Pinchgut. The bad guys were popped out here in Colonial times to cool off. Seldom fed pinch gut grew slowly on them as they harvested out the sea weed and shells. A swim amongst the sharks was not an option.
We are scouting up some more details on the guns, gundecks and in particular the magazine design. You can take a ferry from Circular Quay to the Fort and do a self tour or register and do something more formal. There is a cafe as well. And the views, maaate you are looking at them.