Aboriginal art tours, Arnhem Land: Inside the world's oldest art gallery

The sinuous, six-metre creature might be a rainbow serpent, but looks more like a monster from a B-grade movie, a crocodile-shark with jaws agape, dagger teeth exposed. If this had been painted by Picasso, it would be famous. If it had been analysed by Freud, we'd know about it. A Banksy like this would be all over social media.

This rainbow serpent, though, has no title. It might not even be a rainbow serpent. Its artist is unknown and provenance obscure. It writhes across the ceiling of a rock overhang in West Arnhem Land, exposed to the weather, virtually unvisited. Yet it's an impressive work of art, and just one of tens of thousands of artworks in this corner of the Northern Territory largely ignored by Australians.

Maybe we can be forgiven for not knowing Arnhem Land holds Australia's most fabulous rock-art. Even local Indigenous people have forgotten about much of it. The rainbow serpent was rediscovered in the early 1990s by former buffalo hunter Max Davidson, quite by accident.

In 2012, archaeologists came across what turned out to be the oldest (28,000 years) and one of the biggest rock-art galleries on the continent. As recently as 2017, Indigenous rangers conducting dry-season burn-offs in West Arnhem discovered hundreds more rock-artworks.

Still, it's shocking that many Australians have heard of the Lascaux cave paintings in France but few can name particular rock-art sites in Australia. Australia has more rock-art than anywhere else, and in better condition. It's the oldest, most long-running cultural record on the planet. Even more thrillingly, the descendants of the people who created this art are still around to appreciate and interpret it.

Arnhem Land is where the famous X-ray style of painting originated, which depicts animals' bones and internal organs. There are more reasons than that why its art is superb, though. The rock-art of nearby Kakadu is better known but less varied and not nearly as old. These are more than just paintings that depict the surrounding environment and the artists' own culture. rock-art is a connection to ancestors, to the time of creation, to a spiritual dimension of which outsiders can only be dimly aware. Still, you can feel its timeless energy in this elemental landscape. Sometimes it makes the hair on your neck prickle.

One top spot is Injalak Hill 90 minutes northeast of Jabiru, just beyond Kakadu National Park's eastern limits. It has five rock-art galleries and scatterings of individual paintings. There are creation spirits and evil spirits, kangaroos and long-necked turtles. There are spirits elongated as Giacometti sculptures, and white kangaroos with red skeletons, and abstracts to rival modernist art. They explode overhead in ochre, red and mustard-yellow.