The cache is not at the posted coordinates
Bong Bong Obelisk
The Obelisk is a commemorative monument paying homage to the first settlement in the Southern Highlands in 1821.
To find this cache:
At the posted coordinates you will find three plaques bearing significant dates. Use these dates to calculate the final location.
S 34 31.ABC E 150 23.CBA
A = The sum of the first and third digits in the year the Lombardy Poplar was planted by Prince Richard.
B = The second digit in the year the other tree was planted by Prince William.
C = The final digit in the year the Obelisk was donated by H. Talbot Sanderson, Esq.
Checksum S=31, E=31