Ulu Temburong National Park, located in the heart of a 500-sq-km area of pristine rainforest covering most of southern Temburong, is a highlight of a visit to Brunei. It's odd that a small country such as Brunei should contain such a sizeable chunk of true untamed wilderness. 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.
Ulu Temburong's forests are teeming with life, including as many as 400 kinds of butterfly. The best times to spot birds and animals are around sunrise and sunset, but you're much more likely to hear hornbills and Bornean gibbons than to see them.