Background Information
Sydney sandstone is the common name for Sydney Basin Hawkesbury Sandstone and is a sedimentary rock named after the Hawkesbury River north of Sydney, where this sandstone is particularly common. It forms the bedrock for much of the region of Sydney.
Between 190 and 225 million years ago, what is now the Sydney region was a large freshwater lake. This lake was slowly filled up by deposits of sand, mud, silt and pebbles, washed in by large streams. Over the millions of years that followed, these sediments were gradually overlaid by others and compressed into rock. Two to 12 million years ago, the area was uplifted above sea level. As rivers flowed across this plateau, they gradually cut valleys into it, leaving narrow sandstone ridges behind. The exposed Hawkesbury sandstone was then subject to weathering by wind, rain, water, and chemicals. The unusual weathering in this and adjoining caves occurs when moisture draws soluble salts out of the rock, carrying them to the surface. Here, salt crystals fret the sand grains away. This type of weathering is most often found in rock overhangs and in caves.
Access
From the car-park, take the lower Headland Track, which starts near the end of the swimming enclosure and follows the shoreline.
Soon there is a side track on the right ('5' signpost) that takes you up to the base of the cliff. The cave and overhang at the top of the track are known as Dracula's Canteen by locals. The 200 million year old rocks are made of Hawkesbury Sandstone.
Your Task
1 Look at the unusual patterns in the yellow coloured sandstone on the cave's ceiling, said to be formed by Dracula himself, perhaps in the shape of a bat? This is actually a form of salt weathering which is common in coastal regions. It is named after the hexagonal wax cells built by bees in their nests (and also a sweet). What type of weathering is this called and what colour are the rocks?
2 Looking again at the main pattern on cave ceiling above you, there are 2 central parallel lines (formed from weathering) inside of the main feature. Using your compass, do these lines roughly run N-S or E-W?
Now you need to climb up to the first level - it's not quite as hard as it looks, but take your time and be careful. Start in the middle and then walk over to the shelf jutting out on your right.
2a Before you look out at the beautiful view across the Georges River, look down and you will see 2 initials carved into the rock (perhaps two former helpless geocachers who made it this far but then became victims of Dracula's entranced stare).
What are these initials?
3 Still on the ledge, look over to the other side of the cave and you will see that the rock layers are tilted. Are they titled down Right-Left or Left-Right ?
Descend back down and continue on the track for a few metres to another cave with similar weathering.
4 Start to head back down to the main track. After you go down the first 3 steps (and before the next 4 steps) there is a small track on the left which leads to another cave. At the entrance to this cave look to the right and you will see some unusual circular holes formed from weathering. One of them is almost perfectly round (the one which would be at waist height if you were standing beside it). Climb up to it and measure its width. How wide is it? But beware the monster waiting to leap out from its hiding place in the little hole beside it.
So that you don't make Dracula angry 
please submit your answers via a message for review before you log your visit.
That's it - you've conquered Dracula's Canteen 
NOTE: You need to wear walking shoes with a good tread & you need to bring a ruler and a compass (or smartphone with compass app).
First to Find - JordsAU & Morry9; - Congratulations on a very quick FTF at 3am! Dracula wasn't used to seeing humans entering at this dark hour and you caught him unawares. 
References - Oatley Park Walking Tacks (Hurstville Council); Sydney Sandstone; Sandstone Weathering (Wikipedia)