A freezing wind rushes through the narrow gap in the small cave, whipping rain against my exposed leg as a thick fog descends a few metres away.
Cursing having volunteered to sleep on the outside, I huddle inwards and make a vain attempt to wrestle some of the damp sleeping bag from Phil, who is snoring gently beside me. He grunts and shuffles over the hard rock further into the darkness.
The first day of a planned bracing hike among the sweeping green mountains and valleys of the national park of Chapada Diamantina has been hampered somewhat by our remarkable ability to inadvertently return things to nature.
A pair of sunglasses, some skin cream and one of our sleeping bags all now lie somewhere deep in the burnt orange waters of the fast-flowing Capivari River that is gushing along below our temporary bed.
Our arms and legs are adorned with scratches that still smart after fighting our way through razor-sharp long blades of prickly grass, while one of Phil’s shins now boasts an angry-looking red gash – a souvenir from narrowly missing a fall of hundreds of feet after slipping from a wet rock.
“A couple of years ago I found the skeleton of a guy who had gone missing 17 years before,” our dread-locked guide, Val, had matter-of-factly told us earlier that day. One of the annual victims of this beautifully raw but potentially hazardous landscape.
Trek-induced injuries aside, amid the swathes of lush vegetation covering the expanse’s vast peaks and troughs, around 3,000 waterfalls, rivers, lakes and underground pools wait to be explored.
Perhaps the most famous of these is the Cachoeira da Fumaça (Smoke Waterfall), which at an altitude-sickness-inducing 380 metres is one of the highest in all of Brazil.
On day three of our trek I find myself lying prostrate on a ledge, clutching on for dear life as I peer over the edge to witness first-hand the dizzying drop from the top.
The misty spray that gives the waterfall its name is thrust upwards by huge gusts of air, brushing against my goose-pimpled skin.
After spending a couple of nights in the tiny haven of Vale do Capão we set out on the 25km return leg of our journey to the park gateway of Lençóis.
Bright wild orchids of every colour, zippy lizards and rock formations that haven’t changed over millions of years line the narrow trail, which was first carved out in the 1840s by diamond prospectors who scoured the land for the tiny but lucrative keys to their fortune. In its entirety, the trail stretches all the way to Rio de Janeiro.
Competition grew so fierce, Val says, that when the last plane carrying precious stones out of the area crashed during the 1980s – the rusty engine of which can still be seen abandoned in a crevice – a bloodthirsty war broke out.
Seeing the effect prospecting was having on the land and its people, the government outlawed the practice and in 1985 made Chapada Diamantina (Diamond Plateau) a protected conservation area.
Families who once made their living locating the gems have had to turn to farming or the growing tourist industry to get by, and some are lobbying the authorities to permit controlled diamond panning.
As we follow the historic trail, piles of neatly arranged stones where the garimpeiros – diamond prospectors – had spent days carefully sifting through the rocks still lie undisturbed alongside, a tantalising reminder of the riches lying beneath our feet.
But this is a land whose nature is just as precious. Val stops to point out a small burst of white flowers called Sempreviva – a unique plant that once picked can survive in the same condition for 70 years. It fetches a high price in bouquets but staunch eco-tourism regulations mean it is illegal to remove it, at risk of jail.
Wading knee-high through watery marshes and clambering down steep raspberry ripple-coloured rock, we arrive back in Lençóis just as the sun disappears behind peach-hued clouds.
Hearing the drone of cars and motorbikes, music and chatter, I feel sorry to have left behind the tranquil peace of the park, where silence is disturbed only by the chirp of a bird or the distant running of water.
I reflect on the hair-raising moments of our journey deep into nature as I get ready to sleep that night and resign myself to the fact I will probably never be an athletic, outdoor adventurous-type. But the pleasure to be had from lifting aching legs onto a soft, dry bed is a fair alternative.