Barrens Hut was for decades the signature boat dive of southern Sydney and the site most Port Hacking charters visited. It lies only a few hundred metres off Royal National Park, opposite the southern end of Bundeena, and takes its name from a squatter's hut built long ago into the side of the cliff. The reef runs out from the rock platform with its top at 12–16 m and then drops off to a sandy bottom at up to 28 m; the average dive depth is about 24 m.

The walls are completely covered with plant and animal life – giant ascidians, sea fans, soft corals and sponges – and the sand at their base is dotted with purple ascidians. The best-known features are The Cave and The Tunnel. The Tunnel runs from the sand back under the reef and climbs to the right, and an alternative chimney exit requires a short vertical ascent before angling up at 45 degrees.

Along the wall to the north are more overhangs and big boulders. The fish life is abundant and includes the site's famous friendly blue gropers, many species of wrasse, schools of yellowtail and one-spot pullers, kingfish, eastern blue devils, cuttlefish, snapper and bream, with Port Jackson sharks resting on the sand from July to September. McFadyen notes the donut nembrotha nudibranch, normally rare, is seen here.

Average visibility is about 15 m, sometimes over 30 m, because the site is far from urban runoff. Because of the depth, bottom time on air is only about 25 minutes, and McFadyen reckons you need at least ten dives to appreciate the site properly. Since no charter boat now operates permanently from Port Hacking, the site is dived far less than it once was.

It suits Advanced divers, ideally on nitrox, who enjoy walls and swim-throughs.

Boat only. Launch in Port Hacking (Gunnamatta Bay/Tonkin Park at Cronulla, Lilli Pilli or Bundeena ramps), run out through the entrance and turn right (south), passing between Jibbon Bombora and Jibbon Head in suitable weather, then follow the Royal National Park cliffs south. Barrens Hut is only about 2 km from the entrance, immediately opposite the southern end of Bundeena township – 5–10 minutes.

McFadyen's GPS is 34° 05.4217' S 151° 10.4525' E; the traditional mark lines up the distinctive Cape Cod-style house at Bundeena with terrain features. Run in towards shore watching the sounder and anchor on the reef top near the drop-off.

The Royal National Park coast south of Jibbon faces east and takes swell from the north-east round to the south-east; southerly swell partly wraps around. These sites lie close to the cliffs, and the shallower ones need calm seas so that boats can anchor near shore and divers are not caught in surge – plan on seas under about 1–1.5 m. Westerly and north-westerly winds give the best conditions; a strong north-easter makes the return to Port Hacking rough.

Visibility is generally good because the coast is far from urban runoff, typically 12–20 m, occasionally 30 m. Barrens Hut is close to Port Hacking and partly sheltered by Jibbon Bombora from the south, so it is workable more often than sites further down the coast. Average visibility is about 15 m, with 21 m (January 1996), 25 m (May 2010) and 30 m (July 2014) recorded.

Surge is minimal at 24 m but the shallower reef top feels easterly swell.

Descend the anchor and swim east to the sand at 24–28 m with its purple ascidians, find The Cave, then the entrance to The Tunnel, which runs from the sand back under the reef and climbs to the right (an alternative chimney exit rises vertically, then at 45°). Follow the wall north past overhangs, then return along the reef top. Allow about 25 minutes on air.

Nitrox (EAN28–32) extends bottom time.

Formerly the most dived Port Hacking charter site, but with no permanent charter boat now operating out of Port Hacking it is dived mainly by private boats and the St George Scuba Club.