The Deep Wall is Bare Island's serious dive, a prominent reef face south-west of the island's western point that drops more than three metres onto sand at 15–19 m, with overhangs, cracks and a small cave along its length. It is the deepest of the routes McFadyen has mapped around the island and links the whole system together: from the wall you pass the isolated Big Rock, a sand gully marked by a concrete block that anchors the Energy Australia cable from La Perouse to Kurnell, the 15 Metre ('Boomerang') Reef and, further north-west, the Isolated Reefs, before rejoining the main Bare Island Right reef at Sea Horse Corner. The colours on the wall are described as fantastic – sponges, sea squirts and gorgonians in profusion – and the deeper water brings a different cast: pygmy pipehorses, red Indianfish, big-belly seahorses, dwarf firefish, cuttlefish, bearded cod, morwong, snapper, crayfish under the ledges, Port Jackson sharks in season and, occasionally, a grey nurse shark cruising through.

Weedy seadragons are seen in the kelp on the way out. The dive is demanding by shore standards. Currents in the 16–19 m range often run opposite to expectation, particularly on the ebb after a big high tide; the reefs run in all directions and it is easy to get lost in poor visibility; and if you do surface out here it is a long swim back among fast boats.

McFadyen recommends many dives on the shallower parts of the reef before attempting the full route, a 12 L tank and 50–60 minutes minimum, with 80 minutes typical for experienced divers. Charter operators also drop divers on it by boat and drift the half-circumnavigation back to the bridge. For advanced divers it is the best of Bare Island – deeper, clearer, more colourful and far quieter than the training zones.

Bare Island is part of Kamay Botany Bay National Park, 20 km from the CBD. Drive down Anzac Parade to the La Perouse loop and park on the edge of Anzac Parade as close to the island's access road as possible (arrive before 8 am on weekends). Gear up at the car, walk 200 m down the access road and across the timber footbridge to the island, then down the stairs to the rock platform.

Walk right along the platform past the boat ramp to the island's western point (flat seas needed) or enter at the natural pool nearby on a higher tide. Swim south-west/south-south-west about 15 m on the surface, descend and follow the bottom as it slopes from 2 m to 8 m within two minutes and then to the wall at 15–20 m. Return the same way or via the 15 Metre Reef and main reef to the boat ramp.

Boat divers anchor at 33°59'35.4"S 151°13'47.6"E and dive it as a half-circumnavigation drift.

Diveable in virtually all seas including south-easterlies, but the western point entry needs flat water – use the Pool or the boat ramp otherwise. The main hazard is current in the 16–19 m range, strongest on the outgoing tide after a big high and frequently flowing opposite to what you expect; dive on the high or flood. Visibility on the deep reef is often 15–20 m, far better than the shallows, and was recorded at 4–5 m routinely before 1999.

After heavy rain expect 1–2 m. Boats and jet skis cross the area – never surface away from the island.

From the western point descend and follow the slope to the wall; keep it on your right heading north-west past the overhangs, cracks and small cave, the Big Rock and the former Admiralty anchor site. Cross the sand gully with the concrete cable block north to the 15 Metre Reef, join the main reef at Sea Horse Corner and return north-east along the main reef edge to exit at the boat ramp. 50–60 minutes minimum, 80 for experienced divers; 12 L tank.

Abyss Scuba Diving, Pro Dive and Sydney Dive Academy run it as a guided Advanced/deep-navigation dive most weeks; independent divers who know the site; boat drops by Abyss and Sydney Dive Academy.