The Cross-Borneo Trek: A World-class Adventure
Borneo offers one of the world's greatest adventure-travel routes. East and West Kalimantan are divided by the Muller mountain range, which also serves as the headwaters for Indonesia's two longest rivers (sungai). Sungai Kapuas snakes 1143km to the west coast near Pontianak, while Sungai Mahakam flows 930km to the east coast, by Samarinda. Thus by travelling up one river, hiking over the Muller Range and travelling down the other, it is possible to cross the world's third-largest island. Be forewarned, however: this journey holds significant hazards, from deadly rapids to remote and brutal hiking where the smallest misstep could have life-changing consequences. This should not be your first rainforest trek.
Like all good epics, this one comes in a trilogy.
Sungai Mahakam One of Kalimantan's last great river journeys, travelling the Mahakam can easily fill several days in a succession of boats, making side trips into lakes and marshes, spotting wildlife and visiting small river towns. The trek itself begins (or ends) at Tiong Ohang, up two boat-crushing sets of rapids from Long Bagun.
The Muller Mountains You do this jungle trek for the same reason you climb Mt Everest: because it's there. Noted for its river fording, hordes of leeches and treacherous slopes, the route requires the knowledge of a professional guiding company. If you walk a taxing eight hours a day, you can make it across in five days, but seven is more comfortable and safer. Budget for 10.
Sungai Kapuas The hulu (headwater) region of the Kapuas is home to many of Kalimantan's best and most accessible longhouses. However public-boat travel below Putussibau is nonexistent, meaning most trekkers fly or bus between Pontianak and Putussibau.
Debate rages as to which direction is preferable. The consensus seems to be that east-to-west is logistically simpler, while west-to-east is physically less brutal. Either way, success is a noteworthy achievement you'll remember for the rest of your life.