Brunei's 1288-sq-km Temburong District is physically separated from the rest of the nation by Sarawak's Limbang division, and happens to contain one of the best preserved tracts of primary rainforest in all of Borneo. The main draw is the brilliant Ulu Temburong National Park.
For now at least, the journey from BSB to Bangar, the district capital, is an exhilarating speedboat ride: you roar down Sungai Brunei, slap through the nipa-palm-lined waterways and then tilt and weave through mangroves into the mouth of Sungai Temburong.
Look at Google Earth and the contrast of Temburong's roadless virgin rainforest is easy to distinguish from Malaysia's massively logged and eroded territory. Until not long ago, almost all of Borneo looked like this.