Kalimantan is the Indonesian part of Borneo, which is the third largest island in the world after Greenland and New Guinea. It is located north of Java, west of Sulawesi, and east of Sumatra. Indonesia shares Borneo with Brunei and Malaysia. The sovereign state of Brunei, located on the north coast, comprises about 1% of the land area. The Malaysian states of Sabah and Sarawak in the north occupy about 26% of the island. Kalimantan covers the remaining 73%, the central and southern regions.
The Borneo rainforest is 130 million years old, making it the oldest rainforest in the world, 70 million years older than the Amazon rainforest. There are about 15,000 species of flowering plants with 3,000 species of trees, 221 species of terrestrial mammals and 420 species of resident birds. Although large areas have been subject to massive deforestation, the remaining rainforest is the only remaining natural habitat for the endangered Bornean Orangutan. Other endemic forest species include the Asian Elephant, the Sumatran Rhinoceros, the Bornean Clouded Leopard and the Dayak Fruit Bat.
The climate is tropical with average temperatures ranging between 23 and 31°C. The island has a high annual precipitation, around 300 mm per year, with a light rainy season between March and May, and a more intense one between November and January. The best time to visit is during the months of September and March.
Kalimantan's total area is 544,150 square kilometers (210,097 sq mi) but it has only 14 million inhabitants and the interior is sparsely populated. There are 74 living languages spoken in the 5 provinces.
Mountains, forests and mighty rivers stretch across the interior but vast areas are literally impenetrable so a great way to travel inland is on one of the rivers, such as the Mahakam River in the East, where comfortable river cruises have been operating from the river port of Samarinda since many years. Alternatively one can decide to use one of the small regional airports in the south as the starting point of a visit, such as Palangkaraya or Pangkalanbun that allow for relatively easy access into one of the National Parks. The latter is close to the Tanjung Puting National Park known for the largest wild orangutan population in the world. It is also possible to go trekking in the Kayan Mentarang National Park, the Apokayan Highlands, and around the eastern reaches of the vast Sungai Kapuas but Kalimantan is clearly for tough adventure travelers only.
The Derawan Islands, in the far northeast are a new diving destination. These islands include Sangalaki, Kakaban and Maratua Islands; each has its own signature and unique attraction.