Be One With Nature
It's odd that a small, regulated country such as Brunei should contain a sizeable chunk of true untamed wilderness. Therein lies the appeal of Ulu Temburong National Park, located in the heart of a 500-sq-km area of pristine rainforest covering most of southern Temburong. It's so untouched that only about 1 sq km of the park is accessible to tourists, who are only admitted as part of guided tour packages. To protect it, the rest is off-limits to everyone except scientists, who flock here from around the world. Permitted activities include a canopy walk, some short jungle walks, and swimming in the cool mountain waters of Sungai Temburong.
The forests of Ulu Temburong are teeming with life, including as many as 400 kinds of butterfly, but don't count on seeing many vertebrates. The best times to spot birds and animals, in the rainforest and along riverbanks, are around sunrise and sunset, but you're much more likely to hear hornbills and Bornean gibbons than to see them.