Fort Banks is a large coastal fortification setup to defend Botany Bay. It existed pre-WW2 but received an upgrade of two 9.2 inch guns around this time. The fort these days is slowly being buried by the drifting dunes and plant life. Indeed finding entrances to it now involves crawing through bushes and contortions to get in. But once inside you’ll find a large underground complex to explore. The photos below come from two visits to the site and I think there is even more to find.
From the surface there are some empty buildings to view. Some of these are actually access shafts to the underground complex. But these are now all sealed and ladders have either collapsed or been removed.
Above is one of the original 9.2 inch guns. Below is what it looks like today. The guns are gone and the pits are now filled in.
As with most abandoned places, nature is claiming back the fort. Below shows some of the buildings on the surface and how they are slowly being buried by the sand dunes.
Underground there is much to find. The apparatus you see in the section below shows the machine used to carting the shells from the armory to the surface guns.
Here are some more images from the exploration of the bunkers. They are filled with rubbish but still hold a lot of their original fittings.
More info from Wikipeadia