The Olgas are named after Kata Tjuta (formerly the Olgas) in Central Australia, because the underwater landscape reminded its discoverers of those great domed rocks. The site is a field of very large boulders interspersed with smaller ones on a sandy bottom at about 24 m, one kilometre offshore from Stack Island north of Kiama. Between the boulders are canyons and open sandy areas, creating a maze-like terrain.

The boulders carry heavy growth of sea squirts, sponges and some gorgonians. Yellowtail and silver sweep school over them, numbfish and large bull rays rest on the sand, and phyllodesmium nudibranchs and sea stars are found on the rock. With visibility around 15 m, the combination of massive shapes and colourful growth makes for dramatic scenery.

The challenge is navigation. Because all the boulders look much the same and there is no distinct wall or reef edge to follow, divers must rely on a compass and careful attention to return to the anchor. The site is also only accessible by private boat, since no charter operator works out of Kiama, which keeps it very lightly dived – a genuine off-the-beaten-track site for Illawarra boat owners. Suitable for Advanced divers with good navigation skills, it is best combined with the shallower Blind Shark Reef near Kiama Harbour for a second dive. Because the site is well offshore with no nearby shelter, boat owners should carry a dive flag, a VHF radio and a DSMB for each diver, and leave someone aboard to watch for bubbles and passing traffic. Launching from Shellharbour Marina is a practical alternative if Kiama Harbour's bar is uncomfortable, and allows the site to be combined with the Bass Point reefs on the way home.

Launch from the Kiama Harbour boat ramp (beside Blowhole Point; concrete ramp, trailer parking and toilets). Kiama is about 120 km south of Sydney via the M1 and Princes Highway. No charter operator runs out of Kiama, so a private boat is needed.

From the harbour run north-north-east past Bombo and Minnamurra to Stack Island (about 5.5 km) and continue exactly 1 km offshore to 34° 37.455' S 150° 52.566' E, roughly 6 km in all. Anchor in the boulders; the site can also be reached from Shellharbour Marina, about 8 km to the north.

An open-water site exposed to swell from the north-east through south-east and to southerly wind chop; it needs a swell under about 1.5 m and moderate winds for a comfortable anchorage and run back to Kiama. Westerly winds in late autumn and winter give the flattest seas and best visibility; north-easterly sea breezes on summer afternoons make the return trip rough. Visibility was about 15 m when documented.

Descend the anchor line and take a compass bearing immediately – the boulders all look similar and there is no wall to follow. Explore the canyons between boulders in a loop or out-and-back on a bearing, returning to the anchor with a reserve.

No regular operator – private boat only (no charter runs from Kiama).