Spot G is a section of the northern Lonsdale Wall named, according to the Scuba Doctor guide, 'by a local diving identity' and with a reputation for being hard to locate: 'some even say it doesn't exist, but it does.' It lies within a boat-length of The Swim Through and shares the same reef top at about 20 m, but the character of the face is different. Here the wall runs north–south with the deep water to the east, and the limestone has fractured into huge splits and cracks, with whole sections separated from the main wall so that a diver can swim between the parent cliff and the detached slabs.

The listing rates the site 20–40 m and describes it as 'a photographer's heaven' for the fish life and the colour, and that is the right way to think about it: rather than a swim along a face, Spot G is a place to settle at 30 m in a crack, light it, and work the walls. The splits shelter southern blue devils, zebrafish, moonlighters and senator wrasse; giant cuttlefish use them in the winter breeding season; and southern rock lobster are numerous under the ledges. The encrusting life – zoanthids, sponges, ascidians and small gorgonians – is as thick as anywhere on the wall.

The depth range is a genuine 20–40 m, and there is no shallow water to retreat to on the reef top, so this is a site for divers already comfortable with deep Heads walls. It is dived on either slack, and as with the rest of the system a live boat, DSMB ascent and firm turn time are the basic conditions of the dive. Operators tend to put experienced groups here or on the adjoining Swim Through when the shallower sections are crowded, and technical divers use the base of the wall for trimix dives.

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 Lonsdale Wall a few metres from The Swim Through; the listing notes it is 'remarkably hard to find' and skippers rely on GPS and sounder rather than transits. 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.

Shot onto the reef top at 20 m. Drop over the lip with the wall on your right (deep water east), descend to 30–35 m and follow the big splits and detached slabs for 10 minutes, then reverse at a shallower level, finishing under the overhangs at 22–25 m. Ascend the face to the reef top, DSMB, drift safety stop.

Base 40 m+; nitrox 28–32% suits the 30–35 m profile, trimix for the base. Drift deco under DSMB.

Dive Victoria Group (Portsea and Queenscliff) – double boat dives to the Heads walls most days of the week, site chosen on the morning by slack-water time and swell; Bayplay Adventure Tours (Portsea) – weekend and holiday charters; Red Boats (Queenscliff) – weekend Heads charters; Melbourne clubs (VSAG, Power House Underwater Club, Scuba Diving Melbourne) run their own boats here regularly.