Adelaide, as discussed, has some gorgeous beaches. This one is Maslin Beach. The cliffs are filled with interesting fossils, the water is (generally) calm, the sand is soft, and like most of the beaches near Adelaide, it faces west so is a perfect place to see the sun go down.
It is also Australia's first legal nude beach, declared so in February of 1975. The clothing optional part of the beach stretches about a kilometre from the cliffs. The rest of the beach is "normal".
Around the point is Port Willunga beach, which is also worth while visiting. I wrote a bit about the Star of Greece shipwreck that is easy to find and snorkel around here: https://bitterswede.com/2019/01/shipwreck/