The Abyss is a large detached bommie with a wall face, sitting just inside the Heads on the Point Nepean side within a boat-length of Devils Drop Off. The Scuba Doctor listing gives its dimensions – roughly 100 m east–west and 40 m north–south – and a wall of 20–40 m facing north-east, with the top at about 15 m; overall range 15–40 m. It is listed as a reef dive rather than a wall dive because the structure can be circled, but the north-east face is a genuine drop.

The listing's caution is direct: the site 'is prone to strong currents and swells and can only be dived during slack water turning to a flood. Because of this, caution should be exercised on this dive but the scenery makes it well worthwhile.' The scenery is the encrusting cover of the Nepean side – soft corals, gorgonians, sponges and zoanthids – on a face that catches both tides, with blue devils and crayfish in the undercuts, boarfish and old wives in the lee, rays on the sand at the base and seals overhead. Because the bommie is freestanding, a diver can use its bulk to shelter from whatever current remains and can navigate simply by keeping the rock on one side.

The Abyss is dived less often than Devils Drop Off but is often the second choice from the same boat, and the two are close enough to be dived in a single slack by a strong group. The depth band of 25–35 m suits Advanced divers with deep experience; the 40 m base is the limit. As with everything on the Nepean side inside the Heads, the dive should end with the flood carrying divers toward Portsea, not with the ebb carrying them out.

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 12 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 12 minutes to the site.

The site is just inside the Heads off Point Nepean beside Devils Drop Off, 10–12 minutes from Portsea Pier. 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. The listing warns the site 'is prone to strong currents and swells and can only be dived during slack water turning to a flood'; in practice that means the end of the ebb.

Shot onto the top of the bommie at 15 m. Drop down the north-east-facing wall to 25–30 m and circle the bommie – about 100 m east–west by 40 m north–south – along its base, returning up the face to the top. DSMB from 15 m and drift inside on the young flood.

Base 40 m; nitrox 28–30% suits; drift deco/safety under DSMB on the young flood.

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.