Borneo is the third-largest island in the world with an area of 743,330 square kilometres (287,000 sq mi) and is the largest island in Asia. The island is divided among three countries: Malaysia and Brunei in the north, and Indonesia to the south.
 
Borneo’s highest point is Mount Kinabalu in Sabah, Malaysia, with an elevation of 4,095 m and the largest river system is the Kapuas in West Kalimantan, with a length of 1,143 km (710 mi). Borneo also has significant cave systems. Clearwater Cave, for example, has one of the world’s longest underground rivers. Deer Cave is home to over three million bats, with guano accumulated to over 100 metres (330 ft) deep.
 
The Borneo rainforest is 140 million years old, making it one of the oldest rainforests in the world. There are about 15,000 species of flowering plants with 3,000 species of trees (267 species are dipterocarps), 221 species of terrestrial mammals and 420 species of resident birds in Borneo. There are about 440 freshwater fish species in Borneo (about the same as Sumatra and Java combined).
 
The Borneo rainforest is one of the few remaining natural habitats for the endangered Bornean orangutan. It is an important refuge for many endemic forest species, including the Borneo elephant, the eastern Sumatran rhinoceros, the Bornean clouded leopard, the Hose’s palm civet and the dayak fruit bat. It is the centre of the evolution and distribution of many endemic species of plants and animals.