A bit more info from the photographer on the cave’s location:
“Nearer the north towards the curve of Geographe bay. Road curved around a bit, mostly with sea in view “
and
“this was at a random pull over on one of the coast roads. Stopped for lunch and just went for a walk (about 20 min). I was at a lookout of sorts, about 6m above ground level with limestone around it. I climbed over & down hoping for a problem or two. . . wow!”