Kiama Blowhole

"The shore", Bass wrote, "showed evidence of considerable volcanic fire" and, on the point, he found, "The earth for a considerable distance round in the form approaching a circle seemed to have given way; it was now a green slope ... towards the centre was a deep ragged hole of about 25 to 30 feet in diameter and on one side of it the sea washed in through a subterraneous passage ... with a most tremendous noise...".