Hole in the Wall is a large sea cave in the limestone reef close to The Gap in Dhilba Guuranda-Innes National Park. The Marine Life Society describes a cave about 40 m wide extending roughly 70 m under the reef, with a sandy bottom, and calls it a 'big cave' with some tight squeezes. It is typically dived on the same tank as The Gap, about 100 m away.

The cave interior is lined with sponges, gorgonians and soft corals that thrive in the shaded, surge-fed environment, and it shelters western blue groper, southern blue devils, wobbegong sharks and other reef fish. Light filtering through the entrance creates dramatic silhouettes, and the sandy floor makes navigation relatively straightforward in the main chamber. A torch is required, and the Marine Life Society warns that the tight squeezes are not for newer divers.

The main chamber is wide enough to feel open, but it is still an overhead environment, and the surge that feeds its invertebrate growth can make it dangerous in any swell. Hole in the Wall suits advanced divers with good buoyancy and some experience of caverns or swim-throughs, visiting by boat on calm days. Combined with The Gap, it offers one of the most distinctive dives on the Yorke Peninsula coast.

Plan the pair as a single, well-briefed dive: agree on turn pressures before entering the cave, keep buddy contact inside where silt can lift from the sand floor, and leave enough gas for the swim along the reef to The Gap. Photographers should bring wide-angle lenses – the contrast between the blue entrance and the sponge-covered interior walls is the shot most divers come home with. Because both sites face south into the swell, check conditions from the Gap lookout by car the day before if you are staying in the park.

From Adelaide drive about 300 km (3.5 hours) via Port Wakefield, Minlaton and Warooka to Marion Bay; Dhilba Guuranda-Innes National Park begins just west of the township (vehicle entry fee, pay online or at the Stenhouse Bay visitor centre). Boat access only from the Marion Bay ramp (25-30 minutes west past Cape Spencer) or Pondalowie Bay (about 15 minutes in settled weather). The cave is about 100 m from The Gap, so the two are usually dived together on one tank.

The southern tip of Yorke Peninsula faces the open Southern Ocean and Investigator Strait, so south-westerly and southerly swell is the controlling factor: most exposed sites need swell under about 1.5 m and are best after several days of northerly or north-easterly winds, which blow offshore along this coast. Winter cold fronts bring big south-westerly swell and strong winds and can close the area for days. Summer afternoon south-easterly sea breezes make boat runs rough, so launch early.

Visibility is typically 10-20 m in settled conditions but drops sharply with swell-driven surge. Cave diving here is only safe in low swell – surge inside a large sea cave can be violent.

Descend outside the cave entrance, torches on, and enter along the sandy floor, staying in the wide main chamber and avoiding the tight squeezes unless experienced. Exit, then swim 100 m to The Gap to finish the tank.

Sea cave/cavern with daylight zone in main chamber; no line required for the main chamber but penetration of squeezes needs cavern skills.

No resident operator; dived on Adelaide shop and club boat trips and by private boats.