Directly beneath the chairlift, the Australian Alps Walking Track struggles up the steep hillside. I wonder if people who hike the full 655km of the trail from Walhalla in Victoria to the outskirts of Canberra sneer at those of us dangling our legs from the metal benches above. Perhaps someone is watching us even now, puffing their way up from Thredbo village, shaking their head at our laziness. I doubt it. We didn’t see anyone heading up the fog-dampened track this morning, only those who – like us – finished their snacks, pulled their beanies low over their ears, wrapped their scarves across their faces, hefted their backpacks, handed over their tickets and jumped on the ski lift.

A chilly wind twists around my legs and the cloud draws close, silently reducing our view to the ground immediately below – a few straggly trees, boulders, yellow grass – and the next chair in front of us, swinging from the lift rope. Beyond the hum of the drive at the bottom, the chairlift itself is quiet. For a moment, between one breath and the next, we’re in a small, eerie world of grey, accompanied only by the clunks and whirs of wind and metal on metal.

Then Emily burps, we laugh, the cloud swirls back and the view of the valley unfurls behind us. There are slashes of treelessness under the chairlifts and in long downhill strips which in snow season would be ski runs. The morning sun catches a ridgeline; silver skeletons of snow gums mark the huge bushfires that burnt through here a few years ago.

Soon the clouds lift beyond our sight, heading off to shroud the higher slopes, leaving us under a warm, blue sky. The trail turns to weathered steel grating, raised above the delicate alpine vegetation. We stop to admire small clusters of white flowers, veined with purple, cupping dew like wine glasses. There’s the lichen on rounded boulders of granite, green on grey, and we note the sharper angles of a big block of quartz in a small streambed. There are swatches of silver in the yellow grass, too, the leaves of snow daisies that bloomed over summer but have now almost disappeared. Some flower species are endemic to Kosciuszko National Park; the continental isolation of Australia and the extreme conditions of alpine areas means that much of the plant life here has evolved independently of other highland and alpine areas of the world.

We go slowly. There are a few other people on the path, but they also go slowly, sometimes passing us in ones and twos, sometimes greeting us as we pass them. It’s not that it’s a difficult walk, there’s just so much to see.

The path splits in two and we detour to a lookout platform wedged between weathered rocks. It offers a view over a wide valley – so shallow it’s barely a valley at all – and the hilltops and ridges surrounding us. It’s obvious here just how little the Australian high country resembles the stereotypical image of a mountain range. There are no pointy peaks or clean lines of a child’s drawing, just an ancient, weathered landscape, topped everywhere by jumbles of exposed granite. The path goes gently down, then wends its way up the hillside opposite, the rust brown steel echoing a dusty purple wash across the grass.

Once down in the valley ourselves, the shape of the land is further revealed: the sweep down from the steep ridge, the flattening out, the tilt towards the sun to our right. The slope channels water into a tiny stream that trickles below a grated footbridge. We stop. A few people pass behind us, sparing a glance at the water, at the valley, then pressing on, up towards the summit. But we aren’t really here for the summit. We’re here for this spot, this water: the source of the Snowy River.

Two years ago, I had the idea of trying to walk down the Snowy River from beginning to end. Now, after months of research and planning, here we are. The Snowy has the highest source of any river in Australia; the ridge of Rams Head Range to the left of the path marks the watershed. A raindrop falling on this side of the ridge falls in the Snowy River catchment and it might – if it survives sinking into the sphagnum moss, freezing in winter, seeping out again into the snowmelt, sneaking through three dams and evading evaporation and irrigation along the way – eventually end up in the outgoing tide of turquoise sea off a sun-gilded beach at Marlo on the Victorian coast. Like a raindrop, we have no idea what lies ahead for us. We don’t even know if it’s possible to walk the river, but we’re going to try.The Snowy here is barely a stride wide and no more than ankle deep. The water is cold and clear, and when I bring a handful to my mouth I can taste cloud-weathered stone and alpine herbs. “And fish wee?” Emily asks, because there are fish here – at the top of a mountain! – mountain galaxias, no longer than a handspan, speckled in the colours of the rocks and grasses. On the mossy banks, yabby holes tunnel down into brown soil. There’s no sign of any corroboree frogs, with their vivid black and yellow marks, but it’s not until we see them a few days later at the visitor centre in Jindabyne that we realise just how tiny and hard to spot these endangered creatures are.

Emily has been struggling with her asthma after a recent cold, so she will head back down to Thredbo and drive around to pick us up at Charlotte Pass. Dan and I weave slowly up to another shoulder of the mountain, looking back to see her light pink hair disappearing behind the grasses and rocks.

A new vista opens up to our left: a large tarn, blue under blue sky, grey under cloud, nestled beneath a rocky spur. This is Lake Cootapatamba, the highest lake in Australia. It’s one of only a handful of cirque lakes, or post-glacial tarns, found on the mainland, formed in the bowl-shaped hollow that occurs at the upper end of a valley where a glacier has scoured out the rock. The lake is cupped in a shallow plain and as we climb we can see how the landscape descends in steps down the mountain. Beyond the lake, there’s a distant, bright red dot: Cootapatamba Hut, a survival beacon designed to catch lost skiers and hikers who come the wrong way off the mountain in bad weather. And beyond that, the blurring blue of other hills – perhaps mountains in their own right – stretching to the horizon.We continue up the side of the glacial valley. I’m keeping an eye out for alpine thermocolour grasshoppers. The Latin name, Kosciuscola tristis, shows the link between them and this area – this is one of the rare, endemic species that helped Kosciuszko National Park achieve a UNESCO Biosphere Reserve designation in 1977. But all we spot are a few large locusts that fling themselves into the air and fly off, making a loud clicking sound and flashing bright yellow wings as they go.

Between scanning the ground for insects and gazing at the view to our left, the distance slips by. Soon we’re standing on Rawson Pass. This is the spot where the path from Thredbo and the track from Charlotte Pass meet, before spiralling up the final ascent to the summit. It sees a lot of foot and bicycle traffic. In fact, until 40 years ago, the road from Charlotte Pass was open to vehicle traffic, too. It wasn’t until the UNESCO Biosphere Reserve designation kicked in that the road was closed to public vehicles.

We stop to use Australia’s highest toilet. “I suppose one of them has to be,” says Dan. The block is not just a convenience for day walkers, or a chance to preserve one’s modesty up here above the treeline; it’s an essential way of managing the mountain’s delicate ecology. I can’t really imagine what would happen to the wildflowers and herb fields if a hundred thousand people had a crap on them every year, but I doubt it would be good. Business complete, hand sanitizer applied (there’s no running water up here), we head on.

As we follow the summit track in a loose spiral, I remember climbing up the ladder to a water slide as a kid. Logically, I know our descent along the Snowy River will not be a hectic, slippery-but-easy tumble to the sea, but the thought amuses me.

Glossy black Australian ravens stand sentinel on the rocks above the path. We pass a man who, terrified of heights, makes it to the end of the path but cannot bring himself to take the final few steps up the stones to the summit cairn. I feel for him, having been similarly incapacitated in the past. I take a photo of his partner – she is the highest person in Australia, but he has still made it to the top 10. She returns the favour, snapping a photo of Dan and me, each with a hand on the cairn. We’re laughing because visibility is currently only about 20 metres, the view from the top of Australia is of the inside of a cloud.

But all morning, we’ve noticed that the cloud hasn’t stuck around in one place for very long. We decide to settle in with a snack and wait it out. Sure enough, after a few handfuls of scroggin, a breeze whips the air clear.

All around, the hills roll back like so much rumpled cloth or tissue paper, pinched into peaks that seem both haphazard and deeply rhythmic. To the east, the line of the track from Charlotte Pass is a light cut across a long slope and there, in the valley, we think we can see the silver glint of the Snowy. I turn 180 degrees. One of the strange things about being so high is that the world flattens out. The horizon could be sea rather than land. Where once a mountain or hill stood distinctive in profile, now lies a ridge of blue, a ripple in the surface, a wave caught before it ever thought of breaking.

Perhaps it’s just the thinner air making me dizzy, but in my exhilaration I think of the Snowy River flowing in reverse: saltwater sucked from the sea, purified as it trickles up over hills and rapids, the roots of the mountain drinking, the mountain growing, a living thing. I think of rain slipping upwards out of the moss and throwing itself off the rocks like grasshoppers, like moths, up into the near-reachable sky.

We pat the cairn again and take another look around before heading off. “That’s the hard bit over,” we joke to each other. “It’s all downhill from here.”