Ulu Temburong National Park is 500 square kilometres of primary Borneo rainforest in Brunei, and the reason it is still standing is oil. The sultanate's bills were paid offshore, so it never needed a timber industry, and the forest its neighbours cut and burned was left where it was. More than 70 percent of the country is under trees. When Brunei declared its first national park here in 1991, visitors were held to one corner of it, which is the corner you see, and it still is. Temburong is cut off from the rest of the country by a strip of Malaysian land taken by Sarawak's rajahs in 1890, so the park sits inside an exclave. Until a thirty-kilometre bridge opened in 2020, reaching it meant a boat across the bay or four checkpoints.
The last hour takes you up the river in a narrow Iban longboat whose boatmen read the rapids and gravel bars by eye and thread between them at speed. The hull scrapes stone in the shallow stretches, water comes over the low sides, and the jungle closes overhead until the river is a green corridor. Then comes the walkway. Aluminium ladders caged in wire mesh are bolted into the ridge in stages and climbed one person at a time, until the trunks you were walking under are beneath your feet. Narrow plank bridges hang on cables from tower to tower, flexing with every step, with nothing below the gaps but layers of canopy. Just after dawn the gibbons whoop in the valleys, mist lifts off the ridges and a hornbill crosses the gap beneath you; by midday heat haze has softened the far green. Down in the forest below the towers, clear water slides over black rock into pools cold enough to be a shock in the humidity. Wading into the current, clothes and all, is the customary end to the day. What the closed nine-tenths hold is mostly unseen. Work from the field centre inside the park found that a single tree here can carry four hundred species of beetle, most of them living metres above anyone's head.