A short offset multi at South Cottesloe Beach.
At the posted coordinates you'll find a plaque dedicated to the Elizabeth, a wooden barque that ran aground near this spot after leaving Fremantle for Sydney in the 1800's.
To deduce the final coordinates you'll need some numbers from this plaque.
The geocache is hidden at S32° 00.ABC E115° 45.DEF where;
A = Second digit of the number of crew.
B = The third digit of the ships tonnage.
C = Number of letters in the name of the city the ship was built minus one.
D = Number of passengers divided by two.
E = The first digit of the ships tonnage.
F = Last digit of the year the ship was built.
The checksum of A+B+C+D+E+F = 22
You're looking for a mint tin.
Happy hunting.