Longnose Reef combines a shallow inshore reef with a seaward drop-off. The Marine Life Network describes it as a 5–30 m site with 'shallow inshore reef and seaward drop-off' and places it on the west coast, while Oceanatik puts it off the northern coast and describes wall and reef 'rich in hard and soft corals' with abundant marine life – 'a very exciting dive with lots to see and explore along the walls'. Oceanatik notes that because of depth and mild currents, beginner divers should dive with instructors or groups.

The structure gives divers a choice. The seaward wall is where the depth and the bigger fish are, with hard and soft corals, sponges and sea fans on the face and kingfish, trevally and other pelagic fish in the blue. The inshore reef is shallower and easier and suits the second half of the dive. Norfolk's reef fauna – groper, morwong, rock cod, moray eels, wrasse, butterflyfish, parrotfish and emperors – is spread across both.

The location discrepancy is unresolved: 'north' and 'west' may both be loosely right if the reef lies on the north-west corner of the island, near Anson Point. Either way, the reef is dived by boat and would normally be sheltered in the prevailing south-east trades and exposed to northerly or westerly swell.

It suits Advanced divers comfortable on a wall to 30 m in mild current, and Open Water divers on the shallower sections with a guide. With no chamber on the island, keep the deep section short and plan conservatively.

Norfolk Island is about 1,450 km east of Brisbane; flights run from Sydney and Brisbane (about 2.5 h; check the current carrier). A hire car is essential. Norfolk has no harbour: Norfolk Island Diving's open boat is lowered by crane from Kingston Pier (south coast) or Cascade Pier (north-east coast), whichever is in the lee of the day's wind, and divers board from the pier steps once it is in the water.

North-coast sites are normally reached from Cascade Pier (end of Cascade Road, about 10 minutes' drive from Burnt Pine): the boat runs north-west along the cliffs to the Duncombe Bay area below the Captain Cook Monument, roughly 15–25 minutes. The coast here is within or beside Norfolk Island National Park.

Norfolk's north coast, from Duncombe Bay west to Anson Bay, is in the lee of the prevailing south-east trade winds, so it is the most reliable part of the island for much of the year. It is exposed to northerly and north-westerly winds and swell, more common in summer, which break on the cliffs and pinnacles and cause strong surge. Anything over about 1.5 m of northerly swell closes the boat sites; the beaches need a flat day.

Visibility is typically 15–45 m and often best in winter. There is no stinger season.

Descend on the seaward drop-off and follow the wall at 18–25 m, keeping it on one shoulder and watching the current. Turn at half air and return along the shallower inshore reef for the second half of the dive and the safety stop.

Norfolk Island Diving (local instructor James and divemaster Mitch Graham) – small open boat craned in at Kingston or Cascade Pier depending on wind; runs part-time, mostly weekends, so book ahead by email (norfolkislanddiving@gmail.com).