The Container Wall is the breakwater built in the 1970s to shelter the Port Botany container terminal, when Sydney's port trade moved from Port Jackson to Botany Bay. It was made by piling concrete blocks and tors on a granite base, and below the waterline the gaps between the tors have become a myriad of caves and tunnels. The southern, bay-facing side has the largest cave systems; heading south from the anchorage and then west around the corner the tunnels grow larger, some running 20–30 m through the structure without opening to the water, with multiple entrances and exits and a few sections that require surfacing between tunnels.

It is dark under the blocks and a torch is essential. The attraction is fish: huge mulloway (jewfish) up to 1.5 m shelter in the tunnels, bream and luderick grow to 75 cm because nobody can fish inside the wall, and crayfish are usually present, along with the general run of bay species. As a dive it is closer to a wreck penetration than a reef, with real dead ends that require backtracking and a large number of fishing lines hanging down the outside from anglers on top.

Shore access is over the tors from the Molineaux Point car park and is genuinely dangerous – steep, sharp-edged concrete with falls of two or three metres possible – and the car park has a history of theft and vandalism, so most people come by boat and anchor 5–10 m east of the end of the wall. It is a curiosity rather than a classic, suited to experienced divers with overhead-environment sense who want to see the biggest mulloway in Sydney, and completely different from anything else in the bay.

Shore: drive to the car park at Molineaux Point at the end of Prince of Wales Drive, Port Botany, and climb down the piled concrete tors to the water – it is steep, with 2–3 m falls possible, and the car park has a record of vehicle break-ins, so leave nothing in the car. Boat: from the Kyeemagh or Foreshore Road ramps, 5–10 minutes; anchor 5–10 m east of the end of the wall at the GPS mark. Take a torch and a small tank; the dive is all under the structure.

Inside Botany Bay and sheltered from ocean swell, but the breakwater faces the fetch of the bay and a strong southerly or south-easterly wind builds chop and surge among the blocks; north-westerlies leave it calm. Tidal flow along the wall is mild. Visibility is bay-standard – 3–10 m, better on the high tide and poor after rain – and it is dark inside the tunnels at any time, so a torch is essential.

Port Botany shipping and pilot boats pass close; do not surface away from the wall.

From the boat head south along the bay-facing side of the wall where the largest caves are, round the corner and go west where the caves and tunnels get bigger – some run 20–30 m without returning to open water. Note your route carefully, back out of dead ends, and return either through the tunnels or around the outside, avoiding the fishing lines that hang from the top of the wall. Small tank, torch, no penetration beyond your comfort.

Effectively a penetration dive – treat as overhead; small tank recommended for manoeuvring in tunnels.

No operator; experienced independents and St George Scuba Club only.