Arthur and I are somewhere in Los Quetzales cloud forest, high on the mountain face. We are starting to wonder if we have made a mistake. A jungle after dark is a scary place, full of whispers and insinuation. Spider webs brush across our faces and we have no idea how large or how venomous are the weavers. Roots twist and curl under our feet – or are they snakes? Things fly at us out of the darkness. It has been raining most of the afternoon and the path is slippy, the undergrowth around is thick. Our head torches cast thin beams straight ahead, but the light bounces back off wet leaves and the shadows behind have the glistening fluidity of ink. Every time I look towards Arthur he dazzles me with his torch and I lose my night vision.

This is our first foray into the forest, and venturing out at sunset was misjudged. The girls turned back a kilometre ago and now Artie is starting to get that quaver in his voice that says that his courage is failing. But we are men! We don’t admit fear or acknowledge our mistakes. Misadventure is a burden we must bear. We are still on the trail at least, or I think we are.

“Do you think we should turn back soon Dad?” It is the opening I need.

Happy to go back if that’s what you want…”

“Is it what you want?”

“Well, I could go on a bit. But I don’t want you to be scared.”

“I’m not scared! I just feel a bit tired. Hungry I mean. Hungry and tired.” Next to us in the undergrowth something large suddenly rustles and I jump.

“Jaguar!” I shout. It is intended as a joke but I get the volume wrong and Arthur leaps like a gazelle. His sudden movement startles me, and then we are both running, slipping, slithering our way back down the trail, through the spider webs and over the snakes. We are both hungry and we are tired, but we are not scared. It is time to go home.

We take the trail again at 5:45am next morning. Walking through the forest at sunrise is a whole different experience. Although once again we are in near complete darkness when we start, it is not so terrifying. We can feel the house lights are being gradually raised, black turns to grey and then to drab green. Olive notes show through then mossy tones, it gets brighter, deeper, until finally around us is every shade of green imaginable. At a point we know that the sun has hit the canopy because the leaves are glowing and painted in impossible colours and some have gold lining. The bird song gets louder and wilder. There is a ticking humming, buzzing that seems to rise from the forest floor. We come across gullies and streams, deep clearings with mossy floors, pockets of mist, sudden sunbeams slanting through the trees. We see a toucanet, hummingbirds, a flock of large black and white birds. There are always movements in our peripheral vision.

After about an hour hiking we emerge from the forest at the top of the mountain and into the sunlight. We find ourselves in coffee and avocado fields. A huge valley stretches out below, vultures and eagles circle above. We walk back down the mountain like heroes and have rice and beans for breakfast.

This is the start of our jungle life. By the time we leave Cedrela Eco Lodge two days later, Arthur and I have done the 5km jungle trail four times. We are hungry for more off-grid adventuring. When Menna and I were last in Costa Rica fifteen years ago, our focus was firmly on surfing, bars and beach life. This time around we are chasing nature not waves.

We move from the highland cloud forests of Quetzales down to the humid tropical jungle of Manuel Antonio and see monkeys at last – capuchins and squirrel monkeys – a huge emotional moment for the kids. We meet a tribe of iguanas on a deserted beach, a ranger points out the deadly fer-de-lance, Costa Rica’s most venomous snake, coiled on the edge of a path we have just walked. Fat agoutis scurry past us like dog-sized hamsters. The skies are alive and the kids are constantly spotting new birds, thumbing through their field guides to call out bright yellow kiskadees, hawks on telegraph wires, red tanagers, cinnamon hummingbirds, a pair of lineated woodpeckers. Then – raising the stakes – a pair of macaws blazing a rainbow streak against a misty blue evening (Matilda), a flock of toucans lunching on a fruit tree (Arthur).

We move on to Uvita where we stay in a ramshackle tree house up in the forest and get up close with the darker side of nature. There are scorpions in the beams, we see a poison dart frog on the terrace, a crocodile head surfaces in the lake, huge spiders give Matilda nightmares. We surf on black sand beaches and see more macaws flying against the forest backdrop, blood soaked and screaming murder.

‘More,’ we shout after two weeks of gorging ourselves on nature, ‘Iguanas no longer cut it, monkeys are commonplace. We need bigger game!’ Where are the tapirs and sloths, the anteaters and pumas? Where are the jaguars? We are forest experts now, hardened to insect bites, tuned into to patterns and shapes against the foliage. Our footfall is muffled, we communicate with hand signals, we dress in khaki and strap things to our belts. We need to get into real wilderness.

In the Osa Peninsula, at the southern most stretch of the Pacific coast, there is one vast untamed tract of proper primary rainforest that is said to contain sixty percent of all the biodiversity of Costa Rica and this is where we will head. We need to go to Corcovado.