Gunung Mulu National Park is the most studied tropical karst area in the world. It has 295 km of explored caves which houses millions of bats and swiftlets.[13] The national park is located at 100 km (330,000 ft) from Brunei,[citation needed] lies between the headwaters of Tutoh river and Mendalam river where the latter is a tributary of the Limbang River.[2] The western side of the park are lowland area (38% of the park) and the eastern side are the mountain ranges consists of limestone and sandstone. The landforms in the park consists of rugged summits, steep ridges and escarpments, sheer cliffs, gorges, karst towers, caves and terraces, hot springs, floodplains and waterfalls.[7]