There were certain things I expected to see deep in an old gold mine, but a natural lake you could swim in was not one of them.
The cool water of Mina da Passagem, in Minas Gerais, lies glass-like for miles among the winding galleries 120 metres below ground.
“There aren’t any prehistoric fish living in here, are there?” I check as I tentatively strip down to my swimsuit and dip a foot into the water.
The liquid is clearer than the seas we’ve been swimming in, and eerily disappears into pitch black deep inside the caverns.
We swim over pearlescent rock that shimmers in the artificial light, venturing briefly over to the darker areas before fear of the unknown gets the better of us and we beat a hasty retreat.
A well-heeled Brazilian couple who joined us for the visit look on bemusedly, the woman muttering what sounded vaguely like “crazy English.”
Moments earlier we’d perched on a pulley-operated trolley for the rickety descent into the small dark mouth of one of Brazil’s oldest gold mines.
Founded in the early 18th century, around 35 tonnes of gold were painstakingly extracted from here by thousands of slaves and later by English-made machinery.
Around fifty per cent of the precious metal mined during the boom came from the area’s mineral-rich earth.
We take the bumpy bus ride back to our pousada in the pretty colonial town of Ouro Preto – named after the “black gold” unearthed beneath its misty mountains.
While its near-vertically steep cobblestone roads are a backpacker’s nightmare, once safely installed in a hostel we are free to enjoy its dreamy, romantic setting.
Beautiful, weather-worn Baroque churches funded by the very slaves who once toiled in the mines peep out at every angle among craft stores, restaurants and jewellery shops whose displays glimmer with precious stones.
In the oldest functioning theatre in Latin America, the sounds of drums and a guitar reverberate around the stalls which once hosted the Portuguese Royal family.
The imposing Museu da Inconfidência in the main square is a stark reminder of the miners’ doomed efforts to fight for Brazilian independence when the gold began to dry up.
Our hospitable, silver-haired host, tells us his family have lived in the area for centuries and that he can remember when public transport consisted of a horse and cart – as a child he even had his own pony to get around.
In a small studio down the road, self-made artist Paulo Roberto Valadares continues to paint picturesque scenes every day of the town that has inspired him from the tender age of nine.
Ouro Preto is a place whose history feels as rich as its coveted soil and could well be the hidden jewel in Brazil’s crown.