Few places evoke such a sense of mystery and adventure as Borneo. The third-largest island in the world, it is vast and wild, mostly covered in thick jungle. Malaysia and Brunei occupy some of Borneo, but most of the island is taken up by Kalimantan, a province of Indonesia. Borneo is famous as one of only two places in the world where you can see orangutans in the wild. The only other place they live is the rainforests of Sumatra, also in Indonesia.

Borneo is also home to one of the world’s last remaining great adventures: the Cross-Borneo Trek. The trek crosses the island from east to west, taking in thick rainforest and crossing the Muller Mountains in the middle. This is a very challenging trek, not for beginners – in fact, few Western visitors have ever done it. However, for those experienced and brave enough to take it on, it is a magnificent achievement and an unforgettable experience.

Beginning the Trek: Balikpapan

The Cross-Borneo Trek begins in Balikpapan, the gateway to East Kalimantan. Balikpapan is by far the most cosmopolitan and modern city in Kalimantan. This makes it the perfect place to begin the trek, as you can pamper yourself for a final time before the weeks of discomfort ahead. Balikpapan is easy to reach from elsewhere in Indonesia. Its airport flies to Jakarta, Denpasar, Yogyakarta and other major destinations in Indonesia, as well as internationally to Singapore.

There’s a great range of places to stay in Balikpapan, to suit all budgets. However, we recommend treating yourself at somewhere like the Aston, a luxurious hotel with a great central location. You can read our travel guide to Balikpapan here, for more extensive information on how to get there, where to stay and eat and what to do when you’re there.

Sungai Mahakam

The trek begins in earnest with a trip down Sungai Mahakam, the second longest of Indonesia’s rivers. This in itself is a great adventure, and if you’re not a practiced trekker, or have simply had enough by the time you get to the end of the river, you can turn back having felt like you’ve ventured pretty far off the beaten track.

First, you’ll get a bus or taxi from Balikpapan to the city of Samarinda, a journey of about two hours. There, you can arrange this leg of your journey, although you will probably depart from Kota Bangun, a three-hour bus ride away. Here, you’ll jump on board a ces, a traditional wooden canoe. You’ll travel through rivers and marshes, spotting macaques, potbellied proboscis monkeys, kingfishers, and hundreds more species.

You’ll then board a kapal biasa, another traditional form of river boat, big enough to spend the night as you continue down the river. The boat’s higher elevation also makes for even better wildlife watching, when the light allows. You will then change boats once again for the final part of the journey, this time boarding a fast longboat to manoeuvre the river’s rapids.

You won’t spot as much wildlife on this stretch of the journey, but it’s a pulse-quickening ride. It’s up to you how long this initial river trip takes, but allow at least a few days. You will end up at Tiong Ohang, a small town where you will prepare for your ascent into the Muller Mountains.

The Muller Mountains

At Tiong Ohang, you’ll meet your guide for the next stretch of your journey: the jungle trek across the Muller Mountains. It’s possible to find a guide once you get here, but much better to arrange one in advance. This section of the trek is by far the most challenging: a week-long trudge through dense jungle, alive with leeches and insects but not much else – this isn’t a great wildlife watching experience. More than anything, it’s about the sense of achievement you’ll get after making it through this brutal, unforgiving environment.

Over a week, you’ll wade chest-deep through rivers, scale gorges and hack through the vegetation with a machete, staying at rough campsites en route. It must be stressed that this is a very difficult journey and not to be taken lightly – you need experience, and a guide. Make sure that you wear appropriate clothing and bring first aid supplies and enough food. Be grateful, though, that the same dangers don’t await you as did George Muller, for whom these mountains were named – he made it across them only to have his head cut off by angry locals.

A Final River Trip

Exhausted but fulfilled after making it across the Muller Mountains, you’ll be pleased to know the final stretch of your journey is only a couple of days long. You’ll emerge on the banks of the Sungai Kapuas River, at a village called Tanjung Lokan. Here, you can board a canoe for an exhilarating trip downriver through plunging gorges and rapids, travelling at remarkable speeds until you reach Putussiba.

Putussiba i your first glimpse of modern civilisation for over a week. You’ll can rest for the night before boarding a plane to Pontianak, a large city on Kalimantan’s west coast. Here, your journey finally ends, and you can enjoy the comforts of city life – exhausted, but, hopefully, with a great sense of achievement.

Final Thoughts

The Cross Borneo Trek represents one of the last great wild adventures left in Indonesia, if not the world. The trek in the middle across the Muller Mountains is incredibly difficult; some even compare it to climbing Everest, and certainly fewer Westerners have ever completed it. It is very important that you are sufficiently experienced, use able guides and book with a reputable agency. Do your research, though, and you’ll have the adventure of a lifetime.

Have you ever completed any (or all) or the Cross Borneo Trek? Do you have any suggestions other than those mentioned above? Please let us know in the comments below.