Come on Alex! Nearly there!' Swanto, our Indonesian guide, skips up the hill in his bare feet, jumping between massive tree roots and ducking fronds of vegetation without seeming to break sweat.
Once I've finally caught up with him - and caught my breath - I can start to fully take in my surroundings. Swanto wanted to bring us to this particular spot in the Borneo rainforest, not just because it's beautiful, but because it might not be here in a few months' time. We've just visited another area of forest that has been turned into a huge series of open pit coal mines - and I was shocked by what I saw.
Coal mining is leaving deep scars across Kalimantan, the Indonesian part of the island of Borneo. Trees are being cleared and the land excavated, opening enormous holes in forest and leaving pits full of toxic waste.
Of course, it's not just the trees that are in the way of the mines. Borneo is home to indigenous people, commonly known as Dayaks, who have lived from the forest for generations. Many have lost their land to the mines. In one village, Gagay, the local leader of the Dayak Basap tribe, told us his people have had to move three times to make way for coal mining. In another village, people told us how coal mining had polluted the river that runs past the village. 'Sometimes when we wash, it also feels itchy. More importantly, we can't drink the water anymore,' said Yesmaida, one of the women.
Let's face it, we've all read about consequences of burning fossil fuel, especially coal. However, I couldn't have imagined, until I went to Borneo, how devastating coal mining is for the people living where it happens to be found. Where only a few years ago there were rainforests full of life that sustained local people, I saw huge holes in the earth, the scale so large that the bulldozers working in them looked like children's toys.
On my return to London, home of skyscrapers and the big smoke, I carried out some research into how coal mining is being funded in Indonesia and elsewhere, as part of my role with the World Development Movement. I was horrified to find that the London Stock Exchange holds more global coal reserves than any other stock exchange, and the total value of shares in coal, oil and gas on the London Stock Exchange is a staggering £900 billion. If all of these reserves were extracted from the earth and burned, the carbon emissions released would be enough to cause a catastrophic six degrees of global warming.
UK banks, meanwhile, have lent more money for Indonesian coal than banks from any other country since 2009, and Standard Chartered, the UK's second biggest bank, has lent more than any other bank in the world.
As I remember the lush forests of Indonesian Borneo and the stark contrast of the mines, I am left with the certainty that fossil fuels are disastrous both for the people whose land they destroy, and for all of us because of their effect on climate change. My thoughts are full of the people I met in Borneo, and the destruction of the forests they have known for so many generations. I know that what I saw in Borneo is also happening in many other parts of the world. But I wonder how many people know that it is happening with the help of UK finance?