Thornton Peak is the fourth-highest mountain in Queensland, trailing only Bartle Frere at 1,622 metres, Bellenden Ker at 1,593, and Mount Superbus at 1,375 — and unlike those inland giants, it falls almost to the sea, which makes it one of the most abrupt coastal peaks on the continent. To the Eastern Kuku Yalanji it is Wundu, a presence rather than a landmark. Their connection to this range is not a chapter that closed with European arrival; it is a living relationship, formally recognised in their 2007 native title determination over the Eastern Kuku Yalanji lands. When low cloud snags on the summit and pours down the gullies in slow grey rivers, the mountain looks exactly like what its custodians have always understood it to be: awake, and watching.

Mountains in the wet tropics behave like islands. Their high slopes are cooler and wetter than the lowlands, and the creatures adapted to that chill cannot simply walk to the next peak across the hot valleys between. Thornton Peak is one of only three places on Earth — alongside the Carbine and Mount Windsor Tablelands — where the cinereus ringtail possum survives, a soft grey marsupial that threads the canopy by night and exists nowhere else in the world. Around it lives a whole community of endemic species, plants and animals stranded on this cool summit since the rainforest shrank back during ancient dry epochs. Each is a survivor of a vanished, wetter world, holding on at the top of the only mountain it has ever known.

That isolation is also the danger. As the climate warms, the cool band these species need creeps higher up the slope — and a mountain only has so much height to give. Scientists studying the wet tropics have floated a striking idea: that Thornton Peak, high and cold and steep, might one day serve as a refuge for species being pushed off lower, gentler ranges, a deliberate ark where cool-adapted animals could be moved to ride out a hotter century. It is a sober thought to carry up a mountain this beautiful. The summit that has sheltered ancient life for millennia may soon be asked to shelter it on purpose, the last cold rung on a ladder the warming world is slowly pulling away.

Thornton Peak does not give itself up easily. There is no road to the top and no comfortable trail; the granite boulder-fields near the summit are a maze of house-sized rock and clinging cloud-forest, and the mountain has swallowed more than one traveller. In April 2001, the wreckage of a small Aero Commander 500, missing on a flight along this coast, was finally located on its slopes. The peak rewards distance and respect rather than conquest. From the Daintree River mouth or the warm sand at Cape Tribulation, you look up at a single green wall vanishing into weather — a mountain that has held its secrets, its species, and its sacred name for longer than memory.