North Wall Corner is the hinge of the Lonsdale Wall system. South of here the cliff runs roughly north–south along the western side of The Rip; at the corner it swings through ninety degrees and continues eastward along the southern edge of the Lonsdale Bight reef as 'North Wall'. The result is a two-sided headland of rock underwater, with a face to the east and a face to the north, both falling from a reef top at about 19 m to a base that the Scuba Doctor listing puts at 66 m.

The corner takes the full weight of both the flood and the ebb, and the topography reflects it: the wall is described as 'vertically towering' with big splits and cracks where slabs have separated from the main face, and overhangs at each of the terrace levels. The encrusting life is as dense as anywhere on the wall, with soft corals, sponges and zoanthids, and the splits are home to southern blue devils and – unusually for Victoria – the occasional western blue groper, which the listing specifically mentions. Crayfish sit high under the ledges on the reef top.

What separates this from the rest of the wall is depth and position. There is no shallow terrace to retreat to; the top of the wall is already at 19 m, and a diver who drops over the lip is at 30 m within seconds. The corner also sits partly in the shipping channel, so a live boat, a shipping check with Lonsdale VTS and a strict drift plan are non-negotiable. It is therefore a site for divers with deep-wall experience, and it is one of the standard destinations for Melbourne's technical community, who use the 45–60 m base for trimix dives during the flood slack. Recreational Advanced divers can enjoy the top third of the wall on a short, disciplined dive, but this is not the place to learn the Heads.

Boat access only. Charter boats leave from Portsea Pier (Dive Victoria Group, Bayplay) and Queenscliff Harbour (Dive Victoria Group, Red Boats); run time is about 15 minutes. Private boats launch at Sorrento Boat Ramp (Point Nepean Road, Sorrento, all-tide concrete ramp with trailer parking) or Queenscliff Boat Harbour ramp (Larkin Parade, Queenscliff), roughly 15 minutes to the site.

The site is on the corner of the Lonsdale Wall system just inside the Heads, 36 m east of The Swim Through and immediately south of the channel edge. Skippers must call Lonsdale VTS (Point Lonsdale) or listen to VHF 12 for shipping movements before dropping divers, and must carry a dive flag; anchoring is not permitted in the shipping channel, so a live boat and a drop-shot or drift float is the normal method.

It is dived only on slack water, either at the end of the flood (SWF) or the end of the ebb (SWE); most operators prefer the flood slack so that any residual current sets into the bay rather than out to sea. Slack water at Port Phillip Heads does not coincide with high or low water: it falls roughly three hours after high or low water at Point Lonsdale, and the usable window is typically 20–40 minutes. Use the Ports Victoria / Port of Melbourne slack-water predictions for The Heads (also republished by charter operators and WillyWeather 'Rip Bank') rather than a standard tide table.

Being outside or right at the entrance, it is exposed to Bass Strait swell: anything over about 1.5 m from the south-west or south, or a strong southerly/westerly wind against the ebb, produces standing waves in The Rip and charters cancel. Northerlies flatten the entrance and give the best days. Visibility is best in late summer and autumn (Feb–May) when the water is clear and the westerlies have eased; winter brings 11–13 °C water and bigger swells but often the clearest days after a run of settled weather.

Heavy rain has little effect this close to the ocean. Operators note it is 'generally done on slack water at the end of the flood' for the clearest water.

Drop the shot on the reef top at 19 m at the start of the flood slack. Descend to the corner and choose a side: the north-facing wall runs west–east with the deeper water to the north, the west-facing wall runs south. Recreational divers hold 30–35 m along the first big terrace and its splits; technical divers drop to 45–60 m at the base.

Return to the corner before the current builds, ascend the face to the reef top and complete deco or safety stops under a DSMB while drifting into the bay.

Base of the wall 60–66 m: trimix (e.g. 18/45) with 50% and O2 deco gases is standard for the deep profile; deco must be completed drifting under a DSMB in the channel, so a surface-support boat that tracks the float is mandatory. Rebreather friendly.

Dive Victoria Group (Portsea/Queenscliff) – runs the deep Heads walls for advanced and technical divers on suitable slack-water days; Red Boats (Queenscliff) – deep-wall and technical charters on request; otherwise private club boats (VSAG, Power House Underwater Club, Scuba Diving Melbourne). Not a routine training-boat site.