The Arch is an unusual site for New South Wales: Michael McFadyen points out that it is the only NSW dive he knows where the main feature is made of coral rather than rock. A section of the coral reef outside Lord Howe's barrier has been undermined to create a large archway, and the surrounding area is sand patches, coral and rubble cut by gullies and cracks. The site lies about 1 km south of North Passage and 300 m off the barrier reef.

The boat anchors in about 15 m on sand, and the arch is about 30 m away. It is big enough to swim through comfortably, and McFadyen found large sweetlips sheltering in it. Beyond the arch the route crosses rubble to more sand, then follows a large crack or gully with small overhangs where crayfish and slipper crays hide, before rising over shallower reef at about 6 m. The DAN account of Lord Howe describes 'the Arches' as deep channels with overhangs and side caves through coral, diveable in most weather.

Galapagos sharks are regular here, along with butterflyfish, firefish, leatherjackets, one-spot pullers, trevally, anemonefish, eels and pufferfish. McFadyen saw no nudibranchs, but Howea Divers mention nudibranchs, moray eels and turtles, and light filtering through the archway makes a good photograph. McFadyen recorded 21.4°C and at least 30 m visibility in May.

McFadyen's page for 'Comets Hole' gives the same GPS and description as The Arch, and Diveplanit describes The Arch at 12–18 m about 10 minutes from the shop. It appears that some divers and operators have used the names interchangeably, but Comet's Hole is also a well-known lagoon site, so the two are kept separate here. The Arch suits Open Water divers and is a highlight of the western outer reef.

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 leave the lagoon through North Passage (or Erscott's Passage for the southern end), then run along the outside of the barrier reef on the island's western side. The run is 10–15 minutes. The boat anchors on sand beside the reef, or drops a small float-attached anchor where current is possible.

Lord Howe sits in the path of the prevailing south-east to east trades and winter westerly fronts. The western outer reef lies in the lee of the island in the prevailing south-east to east trades and is dived on most days in those conditions. It is exposed to westerly and south-westerly swell and wind, which arrive with winter fronts (June–September) and can close it for days; north-westerlies also make it rough.

Visibility is usually 30 m or more, falling after big westerly seas stir the sand. Currents are usually light but can pick up near the passages on the tide. Best from October to May.

Anchor on sand at about 15 m. Swim about 30 m to the arch and through it, looking for sweetlips resting inside. Exit north-west across rubble to a sandy patch, then return south along a large crack or gully with small overhangs, checking for crayfish.

Finish north-east over shallower reef at 6–8 m back to the anchor.

Dive Lord Howe (PADI 5-star, 2 Lagoon Road) – morning double boat dives daily in season, afternoon single dives on demand; site chosen on the day by wind and swell. Howea Divers has also advertised dives here.