Duncombe Bay is a cliff-surrounded bay on Norfolk's north coast, below the Captain Cook Monument that commemorates Cook's landing on the island in 1774. Oceanatik calls it 'one of the less dived, yet beautiful cliff surrounded beaches in Norfolk' and describes a shore entry: 'once on the beach, you can drop into shallow waters and make your descent down a gradual sandy slope' to 'a beautiful sandy bottom, majestic wall, and many boulders to explore', with coral-encrusted formations throughout and a maximum depth of 20 m. Norfolk Island Diving highlights the bay's swim-through arches.

The bay is also the base for several of the north coast's boat dives. Cooks Arch sits in Duncombe Bay, Turtle Arch lies to the east of it, the Fireplace is on its eastern side, and Policemans Helmet lies between Duncombe Bay and Anson Point, so a day on the north coast often involves two or three of these sites.

Marine life is described simply as rich, but the north coast shares the Norfolk fauna recorded elsewhere: butterflyfish, wrasse, parrotfish, anemonefish, sweep, groper, morwong, rock cod, moray eels, emperors, kingfish and trevally, with turtles and stingrays, and corals, sponges and sea fans on the rock. Visibility on the north coast is often excellent.

The bay is in the lee of the prevailing south-east trades, so it is often calm when the south coast is rough. It suits Open Water divers, and the gradual slope makes it a good shore dive for newer divers who can manage the walk in. Because access to the beach is not straightforward, a boat dive is the easier option, and the national park setting means there are no facilities.

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. Duncombe Bay is on the north coast below the Captain Cook Monument in Norfolk Island National Park, reached by Duncombe Bay Road from Burnt Pine (about 10 minutes' drive).

The route down to the beach through the cliffs is steep and should be checked locally before carrying scuba gear; many divers visit by boat from Cascade Pier instead (about 15–20 minutes). Once on the beach, you drop into shallow water and descend a gradual sandy slope.

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.

From the beach, descend the sandy slope to the wall and boulders at 10–20 m and follow the wall, exploring the boulders and swim-through arches. Turn at half air and return up the slope to the beach.

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).