Shelly Beach is fantastic and is located in a beautiful part of Sydney. I call it shark city on account for the numbers of port jacksons and wobbegongs I have seen here. There are often dusky whalers seen here although they stay in the distance from divers.
It is an easy dive site and popular with snorkellers too. The entrance via Shelly Beach is easy entry and easy exit, and diveable in almost all conditions as the area is quite sheltered. You can also enter via the Fairy Bower swimming pool area.
For the best experiences do your first dives here as a guided shore dive.
You can have entire dives on the sandy floor looking out for rays, critters and dusky flatheads or you can head over to the rocks and bommies and look for sharks and cuttlefish. As with all dive sites in Sydney there is a chance of boats overhead so please consider this and ensure you have an SMB to launch for ascents.