The Aussie town of Mount Gambier is known for two things: cows and sinkholes.
The land beneath this farming hamlet located between Adelaide and Melbourne
in the continent's southeast corner resembles a 492-foot-thick chunk of
sopping-wet Swiss cheese. Thirty million years ago, this oozing seabed
crawled with invertebrates and was drenched in a sludge of decaying
vertebrates and corals. Time compacted the goo into porous limestone, then
millions of years of rainfall massaged and sliced away at the rock to create
the present-day cave-diving paradise. Ewens Ponds are three shallow
interconnected pools. This secret world contains underwater chambers, ancient
springs and a crater lake that mysteriously changes color each year. Thanks
to walls of limestone — the ultimate pool filter — the visibility can reach
300 feet. Photographing this spot is like shooting topside, but better: Water
magnifies everything. On my most recent dive there, I lay on my back at a
depth of 25 feet while shooting. I held my breath so bubbles wouldn't break
the mirrored surface.