THE Indonesian territory of Kalimantan, with its vast uncharted rainforests laced with mighty rivers, is one of the country’s most neglected and underrated destinations. Comprising roughly three-quarters of the island of Borneo, you can trek for days through Kalimantan’s deep interior without ever seeing open sunlight or any sign of cultivation.

Borneo, the third largest island in the world, hosts the world’s largest arboreal