Somewhere in the jungle of North Sumatra, near a village called Bukit Lawang, a phone was ringing.

Our guide, Roysid, pulled it from his pocket and answered it. I couldn’t make out the conversation, which was in Indonesian. But when he turned to me and said, “let’s go”, I knew immediately.

I was in Gunung Leuser National Park. Roysid was guiding me and a friend on a two-day trek. He’d shown up to meet us at 9am, with his assistant, Hendrick.

All four of us set off into the jungle. It was here, only half an hour in, that Roysid received the call. It was from Hendrick, I’d gathered, who’d slipped away unnoticed. He had news.

“An orang-utan?” I asked Roysid.

“Yes,” he said. “Not far.”

My friend and I looked at each other, eyes wide. This was why we’d come.

Orang-utans live in only two places on the planet: Borneo and Sumatra. But while it’s estimated there are 40,000 to 100,000 left in Borneo, the number in Sumatra is much smaller – 14,000. The chance of seeing one is rare.

In the ‘70s, a rehabilitation centre was set up in Bukit Lawang. When it closed in 2001, the orang-utans, all 229 of them, were released back into the wild.

Today, locals call that group “semi-wild”. They’re monitored by rangers, but live in harmony with wild orang-utans.

Excited, we followed Roysid to a clearing. Two other travellers we’d seen at our lodge are also there, along with their guide and Hendrick – all staring up at the trees.

“There,” Roysid pointed. I craned my neck to look. And then I saw it. High above, in the tree canopy, was a blob of burnt orange. It was moving, and within moments, ducked out of sight.

It hadn’t felt real. To see this animal with which I shared so much DNA (reportedly, 96 per cent) had felt like a dream. So large and so graceful, it had been right above me. How few people in the world would experience such a sight?

The rest of the day passed quickly. We saw Thomas’s leaf monkeys, a great argus pheasant, and a group of black-crested gibbon (“You’re lucky”, Roysid said – he hadn’t seen those in three months).

We were nearly at the campsite before I thought to ask, “Will we see Mina?”. She was a semi-wild orang-utan, notorious for her aggressive behaviour. Roysid had shown us a scar from where she’d bitten his arm.

While rangers are allowed to feed semi-wild orang-utans, guides can feed only four: Pesek, Jackie, Suma and Mina.

“Oh, no Mina,” Roysid said, and we walked on. But not even 15 minutes later, he stopped to pick up a piece of fruit from the forest floor.

“Orang-utan,” he said. “Mina.”

He told us to stay put, while he and Hendrick walked ahead. And there, in the distance, she was. On the ground, and walking towards us. We hid behind trees, and watched as they fed her fruit. Three more orang-utans appeared.

Roysid gestured us to come closer. Another trekking group arrived. It was all happening so fast. Mina, known for her aggression, was just centimetres away. The other orang-utans clustered around us too. My heart was pounding.

Then we were told to go, our audience with the orang-utans over. We were to slip away with Roysid while Hendrick and the other guide continued to feed and distract them.

Another orang-utan crowded onto the narrow path with us, sauntering along. “Mina’s baby”, Roysid said.

At nearly waist-high when fully upright, it didn’t seem like a baby at all. My heart pounded again as I squeezed past the youngster.

That night, as I lay on my mat at the campsite, trying to sleep, my mind raced. I couldn’t shake the mental images of those large, shaggy creatures. They were so human-like, mysterious, and fascinating. Seeing such rare, gorgeous beasts was an experience I’d never forget.

Getting there

Fly into the Sumatran capital, Medan. From there, book a private driver to take you to Bukit Lawang. One-day to 10-day trekking tours can be organised through various companies. I went with Orangutantrek.net.

Where to stay

Hotels and lodges in Bukit Lawang are all relatively similar – rustic and affordable. If you haven’t already booked a tour, you can do so through them. Don’t expect much with the overnight trek accommodation, but it’s the same across the board.

Ecolodge Bukit Lawang is near the start of the trek, and offers a nice, open-air restaurant. I stayed there. On The Rocks Bungalow is another option, even closer to the trek start. Choose from various styles of hut. On the other side of the river is Kupu-Kupu Garden Guesthouse.

The trek

About $170 for two people, which includes:

• One night at Ecolodge Bukit Lawang
• One night camping
• Two lunches, one dinner, one breakfast, coffee, tea
• Permit to enter Gunung Leuser National Park
• Guide for the day’s walking, from 9am to about 4.30pm.

Don’t miss

Lake Toba is a seven-hour drive from Bukit Lawang, but is a popular place to visit while in North Sumatra.

It is an enormous crater lake with an island almost the size of Singapore in its middle. Lake Toba is the largest lake in South-East Asia, and one of the deepest in the world.