Castle Rock is a tower of coral at the Agincourt Reefs, accessible from Port Douglas on a day trip. Rising from 25 metres to almost break the surface, Castle Rock is home to trevally, snappers, sweetlips, goatfish, fusiliers, surgeonfish and a very friendly Malabar groper called Colin!

One of the features of this site is the wonderful healthy hard coral gardens found in the shallows, which are some of the best on the Great Barrier Reef. Exploring these coral gardens divers and snorkelers will find whitetip reef sharks, turtles, lionfish, giant clams and all the typical reef fish you would expect to find on the Great Barrier Reef.