City in Far North Queensland, Australia, that serves as a starting point for people wanting to visit the Great Barrier Reef (6)
I believe the answer is:
cairns
(Other definitions for cairns that I've seen before include "Pyramids of stones as monuments or landmarks" , "Mounds of stones on mountain tops" , "Stone mounds" , "Memorial mounds of stones" , "Heaps of stones - dogs" .)