Comet's Hole is the Lord Howe lagoon site most often used to introduce divers and snorkellers to the island's marine life. Diveplanit places it well within the sheltered lagoon, just minutes from the boatshed, and describes a 3–4 m high coral reef wall around a hole with a median depth of 3 m and a maximum of 7 m. Divernet puts it at 7–8 m, and the DAN account describes it with Erscott's Hole as a circular pool with coral walls.

The variety of fish is what makes it. Diveplanit's list includes swarms of catfish, Lord Howe butterflyfish, doubleheader wrasse, Lord Howe moray, zebra morwong, McCulloch's anemonefish, black stingrays, kingfish, drummer, sweetlips, stripeys, footballers, peacock flounder, angelfish and Galapagos sharks. Divernet adds lined catfish, decorator crabs, three types of lionfish and marble shrimp, with Porites, Acropora and needle corals on the walls. The island pocket guide adds three-striped butterflyfish.

Diveplanit calls it 'one of the easiest dives around' and 'the best possible introduction to the diversity of marine life around Lord Howe Island', and because it is inside the lagoon it is diveable when other sites are not. It suits beginners, courses and snorkellers.

Note that Michael McFadyen's page titled 'Comets Hole' gives the same GPS position and description as his page for The Arch, a 6–30 m coral arch on the outer reef. The lagoon site described here is the one operators and the tourism body mean by Comet's Hole, so The Arch is listed separately. Snorkel boats and the dive shop both visit, so it can be busy mid-morning.

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. The lagoon sites are reached from the Lagoon Road boatsheds: Dive Lord Howe's boat is moored in the lagoon and reaches the holes in about 5 minutes, and glass-bottom and snorkel boats (Islander Cruises, Marine Adventures, Lord Howe Environmental Tours and others) run daily trips.

Snorkellers can also hire kayaks at the boatsheds, but the holes are well offshore near the barrier reef, so a guided boat is the practical option.

The lagoon is protected by the fringing barrier reef on the island's western side and is diveable in almost all weather, which is why operators use it when the outer reef is closed. Strong westerly and south-westerly winds – mainly with winter fronts – make it choppy and push swell over the reef, stirring the sand and cutting visibility. The holes are deep enough to dive at any tide, but the surrounding lagoon floor is very shallow at low tide and boats time runs accordingly.

Visibility is usually around 10–20 m (lower than outside the reef), and water is warmest from January to April.

Divers descend to the sand at 5–7 m and follow the 3–4 m high coral wall around the hole, looking at the anemones for McCulloch's anemonefish and on the sand for rays and peacock flounder. Snorkellers float over the rim.

Dive Lord Howe – lagoon dives used daily as a sheltered option and for courses; snorkel and glass-bottom boat tours by Islander Cruises (daily access to the southern and northern sanctuaries), Marine Adventures, Lord Howe Environmental Tours, Reef N Beyond and Liv For The Sea.