The Mt Mulu National Park is situated close to the southern border of Brunei with Malaysia, about 100km east-southeast of the town of Miri and 100km due south of Bandar Seri Begawan, Brunei. It lies between the headwaters of the Tutuh River, a tributary of the Baram River and covers 544km2, ranging in elevation from 50 meters to 2,376 meters. The park is important for its high biodiversity and unique karst (limestone) features. Besides that, it contains seventeen vegetation zones, exhibiting some 3,500 species of vascular plants. It was first constituted on 3 October 1974 but only opened to public in 1985.
The climate here is determined by the Indo-Australian monsoon system. From December to March, it will encounter the wet northeast monsoon and the slightly drier southwest monsoon from May to October. Generally, rainfall is high here with seasonal averages ranging from 4,000 to 5,000mm. Temperatures in the Melinau lowlands range from 23ºC to 26ºC and at Mt Mulu between 14ºC to 18ºC.