Observatory Rock is the dive most people mean when they talk about Balls Pyramid. The Pyramid is the eroded remnant of a shield volcano, a 552 m blade of basalt rising sheer from the sea 23 km south-east of Lord Howe, and the submerged rock stacks off its north-western corner give divers a sheltered way to explore its base. Diveplanit's survey describes the stacks as five to eight metres high with plenty of shelter between them, from a 5 m top to about 25 m. Nigel Marsh recorded a maximum of 26 m, 45 m visibility, a cave system and a gutter strewn with large boulders.

The dive is a gentle zigzag drift through the stacks. Every crack and crevice holds painted rock lobsters and slipper lobsters – Pro Dive once counted more than 60 slipper crays on a single dive – along with soldierfish, striped boarfish, sweetlips, painted morwong, coral cod and half-banded angelfish. Black coral trees, sea whips and encrusting sponges grow on the deeper faces. Out in the blue, schools of silver trevally, kingfish, rainbow runners and silver drummer sweep past, and the Galapagos sharks that Balls Pyramid is famous for circle constantly; Diveplanit's divers counted more than 60 around them at 5 m during the ascent.

The prize for fish-watchers is the Ballina angelfish, a black-and-white banded angelfish that recreational divers see almost nowhere else. It is usually found deeper but has been recorded here. Bull rays, black cod and the occasional turtle round out the list.

Because the site is open ocean, the boat stays live above the group and there is no reference line on the ascent. That, the remoteness and the current make it an advanced dive, but for divers with the logged experience it is one of the great dives in Australian waters: a genuinely oceanic encounter in 30–45 m visibility, with a seabird-covered spire towering overhead when you surface. Most visitors do it as the first of a double, with South East Rock or Ballina Rock as the second dive.

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.

The boat drops divers up-current of the stacks on the sheltered northern side. Descend to 18–25 m among the 5–8 m high rock stacks and zigzag down-current through the gaps, using the rocks as shelter when the current picks up. Look into the caves and the boulder gutter for painted and slipper lobsters.

Work shallower as air allows and finish with a safety stop in open water under an SMB – this is where the Galapagos sharks usually gather.

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.