Toms Cave is a small feature on the eastern Lonsdale Wall with a distinctive shape: a passage that enters the wall at about 30 m and climbs through the rock to exit at about 22 m. The Scuba Doctor listing describes it as 'a nice little cave dive on Lonsdale Wall' and 'an easy swim through for advanced divers', with 'plenty to see in the area where you exit'. It lies 24 m from The Links, close enough that a group can do both on one slack.

The passage is short and has light at both ends, so it does not require cave training, but it is genuinely enclosed for a few body-lengths and a torch is needed. The rock inside is covered in the same zoanthids and sponges as the outer wall, and crayfish and southern blue devils shelter in it. The exit ledge at 22 m is a good place to spend the rest of the dive: overhangs to either side, old wives and boarfish in the open water, and the wall continuing down to the left for those who want to look over the edge.

The listing restricts the site to slack water at the end of the flood. The depth range of 22–30 m keeps it within Advanced limits and makes it one of the friendlier deep sections, but the top of the wall is already at 20 m and there is no shallow terrace, so bottom time is short and a disciplined DSMB ascent is essential. It is a club and small-charter site rather than a daily drop; Scuba Diving Melbourne and VSAG both record marks for it.

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 eastern Lonsdale Wall beside The Links; an alternative mark from Scuba Diving Melbourne is -38.28958, 144.63798. 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 at the end of the flood (SWF), so that any current after the turn carries divers back into the bay rather than out through The Rip. 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.

Inside the Heads it is sheltered from most swell, but a south-west swell over about 2 m still surges across the top of the wall and a westerly or south-westerly wind over 15–20 knots makes the boat work unpleasant; big seas outside drop visibility to a few metres for a day or two. 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 wall top at about 20 m. Descend to 30 m to the cave entrance in the face, swim the short passage upward with a torch and exit at about 22 m onto the ledge above, then spend the remaining time on the overhangs around the exit. Ascend to the reef top, DSMB and drift the safety stop.

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.