Sunken Rock is one of the Balls Pyramid sites Nigel Marsh logged in his account of diving Lord Howe. He describes a submerged rock with bommies, gutters and ledges dropping from 12 m to 36 m, visited by pelagic fish and Galapagos sharks, and notes it as a place to find the Ballina angelfish. It is less often named in operator material than Observatory Rock or South East Rock and is probably dived when conditions favour its side of the Pyramid.

The layout is a classic pinnacle dive. The top at about 12 m is washed by the open ocean and gathers schooling fish; the flanks break into bommies and gutters that give shelter from the current, and the ledges on the deeper faces are where the Ballina angelfish shelters. Because the rock drops to 36 m, it goes deeper than most Lord Howe dives, and divers need to plan the deeper part carefully.

Marine life follows the Balls Pyramid pattern: Galapagos sharks around the rock and on the ascent, kingfish, trevally and other pelagics in the blue, lobsters in the cracks, and a mix of subtropical reef fish such as sweetlips, drummer and half-banded angelfish. Visibility at the Pyramid is usually 30 m or better, so the scale of the rock and the circling sharks is obvious from the surface.

This is a site for advanced divers with deep experience who are comfortable in current and with open-water ascents. Details such as the exact position and the usual route are not published, so treat the depths here as a guide and follow the guide's briefing on the day. It is worth asking for if you are after the angelfish and the sea is calm.

Lord Howe is reached only by air: QantasLink flies from Sydney daily (about 1 h 50 min), with Brisbane and seasonal Port Macquarie services. Accommodation must be booked before flights (visitor numbers are capped at about 400) and the checked-baggage limit is 14 kg, so most divers hire gear on the island. Dive Lord Howe's shop is at 2 Lagoon Road beside the Lagoon Beach boatsheds; most lodges transfer divers or it is a short bike ride.

Divers board the boat, which is moored in the lagoon, and run out of the lagoon through North Passage or Erscott's Passage, then south past Mt Gower and across 23 km of open ocean to Balls Pyramid – about 45–50 minutes each way in good conditions. Trips cannot be pre-booked: register interest when you book other dives and the shop offers seats when weather and numbers line up (package holders get priority). Allow a week on the island to give yourself a realistic chance.

The run to Balls Pyramid crosses unprotected ocean, so the trip goes only on the calmest days – operators and published trip reports put the limit at winds under about 10 knots and swell under 2 m. South-east trades above 15 knots, any sizeable southerly or easterly groundswell, or a winter westerly front cancel it. Currents around the Pyramid are unpredictable and can switch direction during a dive, which is why it is run as a live-boat drift.

Late summer and autumn (February–May) give the most flat days; winter trips are rare. There are no stingers and cyclones are very rare, but ex-tropical lows can bring big swell in summer–autumn.

Drop onto the top of the rock at about 12 m and descend the down-current side through the bommies and gutters to 25–30 m, searching the ledges for Ballina angelfish. Hold depth only as long as no-decompression limits allow, then work back up the gutters and ledges and finish on the rock top before a free ascent to the live boat.

Nitrox extends bottom time on the 20–30 m sections; confirm availability with the shop. Walls drop well past recreational limits – watch depth.

Dive Lord Howe – Balls Pyramid double-dive charters offered only when weather and diver numbers allow (cannot be scheduled in advance); snorkellers carried if space permits; private charters available. Howea Divers also advertises Balls Pyramid dives.