Cathedral is a deep wall at Holmes Reef. Dive the World describes a wall descending several hundred metres, with grey reef and whitetip reef sharks, turtles, dogtooth tuna, potato cod, Napoleon (Maori) wrasse and golden anthias, and notes that the site was the first Australian sighting location of the golden anthias species found there. Marinelife.org.au combines it with The Abyss as 'The Cathedral/Abyss', while Mike Ball's itinerary map lists both Cathedral and Abyss; this database now treats them as separate sites.

The name suggests towering buttresses and vaulted overhangs on the wall face, a common feature of Coral Sea walls where the reef grows outward into the current. The face is covered in soft corals, gorgonians and sponges, and the depth below the dive is essentially unlimited, so the view down into the blue is part of the experience.

The golden anthias are the scientific curiosity: small, bright-yellow fish that hover in schools along the face, recorded here for the first time in Australian waters. Around them, the big animals of Holmes Reef are on show. Grey reef and whitetip sharks patrol, dogtooth tuna make fast passes, potato cod and Maori wrasse cruise the wall, and turtles rest on ledges.

Cathedral suits intermediate divers comfortable on a deep wall. Because published detail is limited and the site is not on current itinerary pages, it is probably dived only occasionally. The exact position of Cathedral relative to The Abyss is not published, so confirm with the crew which part of the reef is being dived.

Liveaboard only. Mike Ball's Spoilsport includes Holmes Reef on its 7-night Coral Sea exploratory (Cairns return), the 7-night Yongala & Coral Sea expedition (Townsville to Cairns) and the 10-night Coral Sea Odyssey; the overnight crossing from Cairns is about 240 km of open ocean. Holmes is normally allocated a day on these itineraries.

Cathedral appears on Mike Ball's itinerary map and in Dive the World's Holmes guide; it is dived from a mooring or tender drop.

Holmes Reef is a pair of isolated Coral Sea atolls about 240–250 km east of Cairns with no land for shelter. Dive the World calls it a fair-weather destination: SE trades over about 20 knots (common June–August) make the crossing and surface conditions rough, although the lagoons and western sides offer some protection. Currents are normally gentle but can be strong in the channels and on the ridges, especially on a falling tide.

September–December usually has the calmest seas and 20–40 m visibility; December–April is cyclone season.

Descend to 20–25 m on the wall, look for golden anthias and potato cod along the face, then drift or swim slowly along the wall before ascending to the reef top for the safety stop.

Coral Sea liveaboards visiting Holmes Reef (Mike Ball Dive Expeditions) – occasional.