The Caves of mulu
There are several very significant caves in the Sarawak region of Borneo, which is part of the nation of Malaysia. There are a couple of national parks in the Mulu region including Gunung Mulu National Park and Gunung Buda National Park. The caves of the region are still being explored and most of this is done under permit through the joint British-Malaysian Mulu Caves Project. It is also possible to visit the area and tour the caves with a guide. Some of the more significant caves include Clearwater Cave (the 9th longest cave in the world, and largest by volume), Deer Cave (containing the largest cave passage in the world), and Nasib Bagus (containing Sarawak Chamber, the largest cave room in the world).
clearwater cave
Clearwater Cave has a surveyed length of approximately 230 kilometers (143 miles), and is the 9th longest cave in the world. The cave has an enormous average passage size though, and while the estimates on overall cave volume have large error bars, there are no other caves on the top-10 longest list with passage size that rivals Clearwater. So even though the surveyed length of Clearwater is 1/3 that of Mammoth Cave in Kentucky, the overall volume of Clearwater Cave is much larger, making it the largest in the world by volume.
During the 2019 Mulu Caves Project expedition in April and May, several additional kilometers were surveyed, and significant exploration effort went into attempting to connect caves in the southern portion of Gunung Api (the limestone ridge containing Clearwater Cave). Several large caves, including Clearwater, Racer / Easter, and Lagangs, are extremely close to being connected.
deer cave
Deer Cave contains one of the largest cave passages in the world. Deer Cave and Green Cave are bisected by the large doline known as the Garden of Eden. Their combined length is similar, but slightly shorter than that of Han Son Doong in Vietnam, but Deer Cave has a larger cross-sectional area. Deer Cave has been surveyed using LIDAR techniques, but the volume of Han Son Doong is somewhat speculative. Claims about “largest” and “biggest” caves or cave passages has an influence on tourism and the money that brings, so answering these questions objectively can be political.
sarawak chamber
Sarawak Chamber is a large room located in Lubang Nasib Bagus (Good Luck Cave). It is the largest known cave room in the world by area, and roughly equal to the Miao Room in China as the largest in volume. In 2019 we did an overnight trip to Sarawak Chamber to work on an aid climb with the goal of reaching a lead near the ceiling of an obvious fault line. That trip turned into a 2-night stay when rain caused the entrance passage river to rise, which cut-off our exit. The water receded quickly and we were able to exit safely the following morning.