THE CACHE
It will be an easy find for an experienced geo-cacher, but maybe the sea waters will force you to come here more than once to be able to claim the cache with dry feet:) Otherwise, just check the tides beforehand, unless you want to go for a short swimm :)
It is an small container hanging. Be sure to hang it back properly before you leave.
TO CHECK THE TIDES - LINK (http://tides.willyweather.com.au/nsw/sydney/fort-denison.html )
From the cache location you will enjoy the great views over Wolloomooloo, the firger wharf, the naval base, and you will be meters away from the beautiful botanical gardens and it's amazing background of the Sydney Opera House.