'I can't believe this much rainforest gets destroyed every 10 seconds. I just can't believe it," says my 10-year-old son, Louis. We have taken a few steps into the rainforest biome, a giant greenhouse at the Eden Project, and he reads it aloud from the display board at ground level, while funny black birds with red mohawks swagger around the mango trees, eyeing us. He says it again while we tramp up the ramp and walk alongside the tree canopy.

And he says it as we stagger up 64 steel steps to a slightly wobbly perch, 30m above the rainforest’s ferny floor, and look down over the treetops. Our faces are shiny and puce from the 40-degree heat and 80 per cent humidity, and from the climb to our bird’s-eye view (there are boxes near the start of the climb to hold visitors’ coats and bags). You have to hold on to everything, in case your belongings land on someone below – but you cannot hold your breath. You gasp at the noises of nature, the singing birds, the sticky air and the authenticity of the forest environment – “in captivity”, the brochure says – created so carefully under the huge hexagonal plastic plates, or “pillows”, that form the biome.

Twenty-one years ago, this place was a 50m-deep clay pit nearing the end of its working life, leaching gunk and filling with water. Now it is a thriving place where nature is celebrated and curated so that different plants and zones offer a 13-hectare lens through which to view humanity.

Outside, there’s a “zig-zag through time” – a winding path with illustrated panels showing the evolution of the physical Earth and the plants and animals, with our hominid selves appearing at the equivalent of just before midnight on a 24-hour clock.

There are hillocks of daffodils that are replaced by sunflowers and other crops as the seasons rotate. There are vegetable gardens that feed visitors, and occasional nooks and installations to explore and learn about – for example, the processes of mining and the intricacies of the petrochemical industry.

There’s a huge, high zipline (for people bigger than Louis and braver than me) and a giant cushion to freefall on to from a house-high platform (Louis is big and brave enough for this).

There are lovely cafes on the site, with locally sourced, high quality food, thoughtful additions such as kitchen roll on every table, and recycled, sustainable everything.

There are picnic spots throughout, and dogs on leads are welcome. There is a busy education centre, the Core, and there is a shop with every imaginable type of eco-gift, as well as Cornish goodies and stands of arty cards and Nepalese paper.

And then there are the two gigantic greenhouses, designed to sit on and respect the undulating surface of the former pit. We go to the smaller Mediterranean biome first, as there will be a wedding here later. We wonder under which boughs the couple will take their vows. The cacti in the Californian section? The citrus trees or shady figs, the olive groves or grape vines in the southern Europe section? Or will they tiptoe through the 100 types of tulip, and, like my young goalie, spot the “Ronaldo” variety doing its showman thing amid the swathes of colour?

Three weeks after our visit, I ask Louis what struck him most about Eden. “The scale of it,” he says. “What they’ve brought to that space, and what people can take away from it.” That day, his tiny school is awarded its fifth green flag, for biodiversity. It’s a great achievement. And projects such as Eden, which is an educational charity, help to highlight what its creator, Tim Smit, wants us to remember: that “we are a part of nature, not apart from nature”.

To contextualise, for example, the rate of destruction (about 6,000 sq km of Amazonian rainforest were cleared in Brazil in the 12 months to July 2013) and make it understandable and relevant. “Every 10 seconds,” Louis says again.

The Eden Project, Bodelva, St Austell, Cornwall; edenproject.com; @edenproject