Located on the eastern part of Malaysia, just south of Brunei, is Gunung Mulu National Park. The park holds one of the largest known natural chambers, Sarawak Chamber, that sprawls an enormous 700 meters in length, and which is open to exploration by anyone up for a unique caving experience. Also within Gunung Mulu National Park is the extensive Deer Cave passage, one of the largest single cave passages in the world—some would even say that it is the largest cave passages in the world, and of course, it is open to travellers.
Recognized as a UNESCO World Heritage Site in 2000, Gunung Mulu National Park has had countless expeditions explore the surrounding rainforests and extensive cave networks. To date over 20 expeditions have attempted to explore Gunung Mulu National Park and their collective work is cited as the Mulu Caves Project, a collaboration between UK speleologists and the Sarawak Authorities hoping to show Mulu’s importance as an extraordinary and vast underground landscape. Other notable caves in this area are Benarat Cavern, Wind Cave, and Clearwater Cave; which has parts one of the world's largest underground river systems and is believed to be the largest cave in the world.
There are tough but rewarding multi-day hikes available across Gunung Mulu National Park. For more information on exploring this fascinating area of Malaysia check out the Tourism Malaysia page on Gunung Mulu National Park.