Cathedral Cave is one of the most impressive caverns in Jervis Bay – a huge sea cave in the outer cliffs of the Beecroft Peninsula, a little over 5 km north of Point Perpendicular. The entrance lies in a large gap between a prominent rock and the cliff face, at about 12 m, and the floor inside drops to about 18 m. McFadyen estimates the cave at roughly 100 m long, 20 m wide and 10 m high, with a dog-leg to the left extending about another 20 m into total darkness.

The name comes from an air pocket above the water inside, where divers can surface into a vaulted chamber – the 'cathedral'. Visibility inside is typically 20–25 m because the cave is flushed by clear ocean water, and torch beams pick out sponges and encrusting life on the walls. Wobbegong sharks rest on the floor, and in late winter Port Jackson sharks shelter in the cave in numbers. Outside, the wall and boulders to 23 m offer a second phase of the dive with typical Beecroft reef fish.

This is a dive for experienced divers: most of the cave is in darkness beyond the entrance zone, surge can be felt in any swell, and the air pocket should be treated with caution (air may be stale; keep regulators in). A primary and backup torch are essential, and a guideline is sensible for anyone venturing into the dog-leg. On a calm winter day with clear water it is one of the signature experiences of Jervis Bay diving, and it can be combined with Crocodile Head or The Caves, which lie a short distance to the south.

Charters depart Huskisson (Dive Jervis Bay; boats in Currambene Creek). Private boats launch at Huskisson, Callala Bay or Murrays Beach (Booderee), or at Currarong's ocean ramp. From Huskisson cross the bay to the entrance and turn north around Point Perpendicular onto the outside of the Beecroft Peninsula; continue a little over 5 km north of Point Perpendicular to 35° 03' 40.46" S 150° 50' 25.17" E (about 35 minutes from Huskisson).

Anchor on the mark; the cave entrance is behind a prominent rock surrounded by white water, in the gap between the rock and the cliff.

The outer Beecroft Peninsula cliffs face east to south-east and take the full force of any south-easterly or easterly swell; the sites are diveable in swell under about 1.5 m and are well sheltered from south-westerly and westerly winds, which make them the go-to sites in winter. North-easterly winds (common on summer afternoons) make the run from Huskisson across the bay entrance rough and cause surge on the northern-facing cliffs. Visibility is commonly 15–25 m and can reach 30 m in winter when clear oceanic water sits against the peninsula.

Currents along the cliffs are usually mild but can run at the bay entrance on a strong tide change. Defence live-firing closures can shut the sea area – check before going.

Swim from the anchor to the gap between the rock and the cliff, descend to about 18 m inside and penetrate the main passage with torches. Explore the left-hand dog-leg that extends about 20 m further into darkness, surface briefly in the air pocket, then return, photograph the entrance and explore the wall outside before ascending.

Cavern/cave: primary and backup torch; guideline recommended for the dark dog-leg section; cavern training advisable.

Dive Jervis Bay (Huskisson; boats Avalon and Genesis) runs double boat dives most days, and Deep 6 Diving Jervis Bay / other Huskisson operators also visit; site chosen on the day according to swell and wind.