On Tuesday, the sky above Queensland's reefs and rainforests will undergo a brief but dramatic transformation. Just after sunrise, a black mark will appear at the sun's edge and expand to cover its entire disc. Darkness will envelop the strangler figs and pencil cedars of the forests below and engulf the angelfish and wrasse on the Great Barrier Reef. Thousands will visit the region to watch the spectacle and see the sun endure "that darkening of his radiant face", as William Wordsworth once described an eclipse. The solar corona and prominences, normally invisible, will be seen flickering against the inky blackness of space: an unforgettable experience.
But those who visit merely to look skywards will miss an equally extraordinary vision – for the landscape that lies below the eclipse's path is one of the most remarkable on the planet: a juxtaposition of rainforest and a vast expanse of gleaming coral. The former, a chunk of forest left over from the ancient supercontinent of Gondwanaland, is more than 110 million years old. By contrast the Great Barrier Reef, in its current form, only started growing a few thousand years ago.
This is a landscape of incredible diversity – though intriguingly the two habitats have links. For a start, they are contiguous: the sea that covers the barrier reef also laps the beaches that edge Daintree rainforest. You can visit both in a day, though I'd recommend a week and would have happily made my trip last months.
To reach the rainforest, you drive north from Cairns, the main town of Far North Queensland, through sugarcane plantations and grazing kangaroos until you reach Daintree River. Beyond this point, there are no mobile phone signals, no mains electricity and no lavish spa hotels. This is a wilderness, the largest chunk of tropical rainforest in Australia, home of one of the world's oldest flowering trees, the idiot fruit (Idiospermum australiense), and one of the last refuges of the cassowary, a 6ft, blue-throated, flightless bird whose powerful legs and claws can inflict grievous injuries on overcurious humans.
At the Daintree Discovery Centre, a huge tower has been erected along with an aerial walkway so that you look over the forest canopy and peer down at the lineas, rattan cane and orchids, as well as the bright blue Ulysses butterflies that flit around them. It is a perfect introduction to the landscape.
Deeper into the forest, I stayed at the Cape Tribulation Exotic Fruit Farm, which gets its rather splendid name from the local cape where Captain Cook's Endeavour struck a reef in 1770 and which was given the moniker Tribulation as a result, along with neighbouring Weary Bay, Mount Misery and Mount Sorrow. Tourism was clearly not a priority for the great explorer.
I was booked into a timber cottage deep in the forest: ideal for couples seeking isolation perhaps but for a solitary visitor, unused to rainforests, it was unnerving. At night, the place echoes to the howls of creatures such as the black butcher bird which has a disturbing shriek and get its name from its habit of killing small animals, which are then hung from branches beside their nests.
Only earplugs saved my sanity. By contrast, the breakfasts provided by owners Alison and Digby were stunning and included sweet, fleshy star apples and gnarled pieces of rollinia fruit that taste like lemon meringue pie.
There are plenty of animals living in the forest – striped possums and spectacled flying foxes, for example – but they are elusive. By contrast, the birdlife is stunning and for my farewell to the forest I drove to Daintree village to stay at the Red Mill House before heading on a bird-watching cruise on the river that included sightings of egrets, black bitterns, frog-mouthed owls, forest kingfishers and yellow orioles. The river itself is crocodile-infested and you need to take care. On the other hand, there are no funnel-web spiders or other deadly arachnids this far north in Australia.
From Daintree, a visit to the Great Barrier Reef is a straightforward business. At nearby Port Douglas, you can take a catamaran to Agincourt Reef where there is a floating array of viewing decks, restaurants and changing rooms. Human access is very carefully controlled on the reef and this is one of the selected areas permitted for tourism.
Although miles from the coast, the reef here is still only a few feet below the surface and a snorkel dive reveals a glorious panorama of brightly coloured corals: giant blue staghorn branching upwards while strands of spaghetti coral wave in the current. Tiny green fish swim around the softer corals, disappearing inside them when approached. It is a mesmerising experience.
Later I joined Dave, one of Agincourt's marine biologists who guided me to the colonies of blue starfish and hermit crabs and to the shoals of parrotfish, each being groomed by a cleaner wrasse fish. The colour and variety of life here is breathtaking – as is its scale. Covering more than 330,000km2, the Great Barrier Reef is the largest single structure made by living organisms. You can see it from space.
The two habitats on my trip might seem dissimilar but they are connected through the biological processes that sustain them. Every year, eight tonnes of leaves fall to the ground for each hectare of forest in Daintree. Without this leaf-fall, the soil below could not nourish the plants that grow there. Similarly, dying coral polyps create the fabric of the reef on which new coral flourish and provide refuges for the hundreds of fish species that make homes on the barrier. Both habitats share the same sort of symbiotic complexity and biological inter-relatedness.
As the conservationist John Muir once remarked: "When one tugs at a single thing in nature, you find it attached to the rest of the world." That is the real lesson of the reef and the rainforest.
Robin McKie is the Observer's science editor
Essentials
Robin McKie's trip was provided by Tourism Queensland (tq.com.au). Cathay Pacific (cathaypacific.com) flies from Heathrow to Cairns via Hong Kong from around £1,200 return. Two nights' B&B in a double room at Cape Tribulation Exotic Fruit Farm (capetrib.com.au) costs from £235. Red Mill House (redmillhouse.com.au) has B&B doubles from £240 for two nights. Quicksilver (quicksilver-cruises.com) offers snorkelling tours of the Great Barrier Reef
