OH...... I would be showing my travel ignorance if I answered this question. I have loved a lot of the beaches that I have seen. I love the beaches in Far North Queensland, Whitsunday Islands, and Fiji, but haven't travelled great distances to be able to compare beaches. I could not say that any beach I have been to is particularly UNIQUE. Perhaps the bathing boxes on the beaches of the Mornington Penninsula are unique to tourists, but to me, it's HOME
I've only been to a few beaches as I am not a sea side sort of person. I can't say any of them were that unique. My favourite was Little Hampton, which had a pirate crazy golf course. I also went to a pebble beach, which I prefer to sand. The most unique was probably around Grange, which is covered in grass and sand pits due to an infestation of seeds that washed up on shore.
Sadly I have not been to many unique ones :( I do love beaches very much, but my travels have been to cities and towns.
I do have a favorite one in the whole world, as I grew up I spent 90% of my time at this beach, as we lived very close.
Have been to lots of beautiful beaches here in NSW and QLD, California,Bali , Noumea, Port Villa and a few aother beaches overseas, but the most unique and best beach is where i spent 2 months in 2016 is in Fiji on one of the outer Islands in the Lau groups.