Deep in Borneo’s jungle sits Gunung Mulu National Park. Best reached by air from other cities in Borneo, this park in the Malaysian state of Sarawak has four “show caves” that people can visit as part of a regular guided tour. More adventurous caving expeditions for experienced spelunkers include a trek to Sarawak Chamber, discovered in 1980, and thought to be the largest cave chamber in the world.