Whale Bommie is the signature site on Milln Reef and one of the classic Cairns outer-reef dives. It is a single, isolated coral pinnacle that rises from sand at around 30 m to within a metre or two of the surface; on a low tide the swell breaks over the top and throws up a plume of spray that looks like a whale blowing, which gave the site its name. Passions of Paradise refers to it as The Whale and calls the deeper neighbouring outcrop Little Whale, dived by advanced divers to about 24 m.

Because the bommie is isolated and steep-sided, circling it is effectively a wall dive, and the full depth range is available on every side. The walls carry soft corals and gorgonian fans, and operators note a superb stand of black coral on the deepest side. Whitetip reef sharks rest on the sand at the base and in the undercuts, bumphead parrotfish move around the pinnacle in groups, and turtles are regular visitors.

Painted lobsters and reef crabs occupy the crevices. The bommie concentrates fish from the surrounding sand, so schools of fusiliers, snapper and sweetlips are usual, and trevally hunt around it. At night Whale Bommie is outstanding: whitetip sharks hunt actively along the walls, turtles sleep wedged under ledges, and the lobsters and crabs come out onto the open reef.

Its depth makes it better suited to divers with some experience or an Advanced certification, though the upper walls are fine for anyone and snorkellers can enjoy the top when conditions are calm.

Boat access only. Cairns day boats leave from the Reef Fleet Terminal (1 Spence Street) and the neighbouring Marlin Marina on the city waterfront, with check-in between about 7:00 and 8:00 am; most operators run transfers from city and northern-beaches accommodation, and there is paid parking near the terminal. The run of about 55 km out through Trinity Inlet and across the lagoon to Milln Reef takes around 76 minutes on a fast catamaran and noticeably longer on slower dive boats or into a south-easterly chop.

Whale Bommie has its own mooring used by Silverswift, Passions of Paradise (as 'The Whale') and the Pro Dive Cairns liveaboard. Enter from the stern and descend the mooring line to the bommie.

The prevailing south-east trade winds (typically 15-25 knots from April to September) are what limit Cairns outer-reef diving: above about 25 knots trips may be cancelled, and exposed eastern moorings are used only in light winds. Summer northerlies are gentler but make north-facing moorings choppy. Box jellyfish and Irukandji are present from about November to May (stinger suits on every dive), and the cyclone season runs November to April, when a system in the Coral Sea can close the reef for days.

Visibility drops after heavy rain and strong winds; spring is usually calmest and clearest. Because the bommie stands alone, it can be surgy near the top in fresh trade winds and around low tide; it is best at mid to high tide and is one of the most popular night dives on Milln in calm weather.

Descend the mooring to the base on the sheltered side, drop to 20-25 m to look for the black coral stand on the deepest face, then spiral slowly up and around the bommie. Spend the second half of the dive on the upper walls at 8-12 m and finish with a safety stop near the top, keeping clear of surge at the crest.

Silverswift – daily day trips (Milln is one of its core reefs); Passions of Paradise – daily sailing-catamaran trips to Milln moorings; Pro Dive Cairns – 3-day/2-night liveaboard including Milln night dives