Bigge Island, Western Australia: This island in the Kimberley is a true haven

Sweat trickles down my torso in cool rivulets, as I duck beneath the branches of a Kakadu plum tree, seeking refuge from the beating mid-morning sun. I'm trying to focus on our guide, but the still, cobalt ocean winks from the bay below. Daring me to take a dip, crocs and stingers be damned.

"Monjon, monjon!" cries our naturalist guide, a petite brunette named Juliana Restrepro, pointing wildly into the valley below like an exuberant air traffic controller. I spin around, swimming and sweating forgotten, in time to see a small brown furry creature bounce off the rocks and disappear safely into a crevasse.

Restrepro is thrilled. Monjons - the smallest rock wallaby species, that was only discovered in the 1970s and that is endemic to this northwest region of the Kimberley - are usually only seen in the early morning and late at night. We're lucky, she says. And now I'm paying attention.

We're six kilometres from the Australian mainland on Bigge Island, the largest of the Bonaparte Archipelago's islands. Forty thousand years ago, however, before the last Ice Age, this island would have been mainland. "Because of that, there's a lot of the same fauna as the mainland," says Restrepro. "But being an island, invasive and feral species haven't made it here, so it's a natural wildlife refuge."

The more time we spend on Bigge Island, the more I realise what a true haven it is. A few minutes later, Restrepro points into the rugged gully where the monjon vanished, to a long, curved line of carefully placed rocks. "These rocks would have likely been a ceremonial site, probably for men's business, for the local Wunambal Indigenous people."

Similar rock formations exist all over the Kimberley, she says, some of them stretching up to 25 kilometres long. "They usually lead from one place of cultural or spiritual significance to another, but this one could have led to a fresh water source, or to the rock art site we're about to see."

We follow Restrepro down dusky pink, quartz-rich sandstone boulders and over patches of darker grey dolerite, to a stand of tangled mangroves. The ground around them is covered in holes and prints – tiny mounds of burrowed sand from ghost crabs, tracks from monjons and northern quolls, and from birds with toes as thin as brushstrokes.

Progress is slow in the heat, but soon Restrepro gathers us around the mouth of a sandstone cave. The entrance is painted with an imposing white figure with haloes of ochre and white around its head, large dark eyes, and no mouth.

This is the first I've seen of the Kimberley's famous Wandjina art, which depicts ancestral beings that travelled through this region during the Dreamtime. The orbs around the head represent clouds, we're told, since Wandjina are responsible for bringing the wet season rains, and therefore for all creation.