The ten longest cave systems on Earth by documented passage length, from Kentucky's Mammoth Cave at 685.6 km to a 218-km network in Spain.
Mammoth Cave in Kentucky, with 685.6 km of surveyed passage, is the longest cave system in the world. Sistema Ox Bel Ha in Mexico is second at 541.7 km and the Shuanghedong Cave Network in China third at 481.5 km. The ranking uses total surveyed passage length as listed in Wikipedia's List of longest caves on 18 October 2026.
Caves are naturally formed underground voids, and the longest ones are vast networks of connected passages that can stretch for hundreds of kilometres. The best candidates form in karst landscapes, where soluble rock such as limestone is slowly dissolved by groundwater. Because cave explorers keep discovering new passages, these lengths grow over time. This list ranks the world's longest cave systems by their documented combined passage length in kilometres. Only caves with more than 100 km of surveyed passage are included here, and the figures are those in Wikipedia's List of longest caves as of 18 October 2026.
Mammoth Cave in Kentucky, USA, is the longest cave system in the world at 685.6 km of surveyed passage. Located in Mammoth Cave National Park, a UNESCO World Heritage Site, it has been explored since prehistoric times and remains the gold standard in cave exploration. Its vast connected passages continue to yield new discoveries.
Sistema Ox Bel Ha near Tulum, Quintana Roo, Mexico, is the world's second-longest cave system at 541.7 km. It is a flooded underwater cave network typical of the Yucatán Peninsula's cenote systems, explored by cave divers. Its southern portions lie within the Sian Ka'an Biosphere Reserve.
The Shuanghedong Cave Network in Guizhou, China, has 481.5 km of surveyed passage after its 25th international expedition, reported in October 2026, making it the longest cave system in Asia. Discovered in 1988, it is the largest dolomite cave system in the world and lies within the Suiyang Shuanghedong National Geopark.
The combined Sistema Sac Actun and Sistema Dos Ojos near Tulum, Mexico, reaches 387.1 km, ranking it the world's fourth-longest cave system. Sac Actun was connected to the Dos Ojos system in 2018, uniting two major flooded cave networks in the Yucatán into a single system.
Jewel Cave in South Dakota, USA, is the world's fifth-longest cave at 354.59 km. Discovered in 1900, it is protected as Jewel Cave National Monument and is famous for its abundant calcite crystals, including dogtooth spar and nailhead spar formations that give the cave its name.
Wind Cave in South Dakota, USA, has 270.4 km of surveyed passage, making it the sixth-longest cave system in the world. Discovered in 1881 and named for the strong winds at its entrance, it is protected as Wind Cave National Park and is famous for its rare boxwork and frostwork calcite formations.
The Clearwater Cave System in Sarawak, Malaysia, reaches 268.6 km, ranking it the seventh-longest cave network in the world. Discovered in 1978 in Gunung Mulu National Park, a UNESCO World Heritage Site, it is one of the great cave systems of Southeast Asia's karst landscapes.
Optymistychna Cave in western Ukraine has 264.5 km of surveyed passage, making it the eighth-longest cave system in the world and the longest gypsum cave. Discovered in 1966, it is a complex maze of passages located near Korolivka in the Dniester Canyon National Nature Park.
Lechuguilla Cave in New Mexico, USA, has 244.7 km of surveyed passage, ranking it the ninth-longest cave system in the world. Known since 1900, it was a small cave until cavers broke into its vast lower passages in 1986. It lies within Carlsbad Caverns National Park and is famous for its gypsum chandeliers and other rare formations.
Sistema del Alto Tejuelo in Cantabria, northern Spain, reaches 218.5 km, rounding out the top ten longest cave systems in the world. Discovered in 1965, it is a network in the limestone uplands of eastern Cantabria.
| # | Name | Location | Type | Discovered | Protected area |
|---|---|---|---|---|---|
| 1 | Mammoth Cave | Kentucky, USA | Limestone cave | Prehistoric | Mammoth Cave National Park (UNESCO WH site) |
| 2 | Sistema Ox Bel Ha | Quintana Roo, Mexico | Flooded underwater cave network | Prehistoric | Sian Ka'an Biosphere Reserve |
| 3 | Shuanghedong Cave Network | Guizhou, China | Dolomite cave network | 1988 | Suiyang Shuanghedong National Geopark |
| 4 | Sistema Sac Actun / Dos Ojos | Quintana Roo, Mexico | Flooded underwater cave network | Prehistoric | None (near Sian Ka'an reserve) |
| 5 | Jewel Cave | South Dakota, USA | Calcite crystal cave | 1900 | Jewel Cave National Monument |
| 6 | Wind Cave | South Dakota, USA | Boxwork calcite cave | 1881 | Wind Cave National Park |
| 7 | Clearwater Cave System | Sarawak, Malaysia | Limestone cave network | 1978 | Gunung Mulu National Park (UNESCO WH site) |
| 8 | Optymistychna Cave | Ternopil Oblast, Ukraine | Gypsum cave | 1966 | Dniester Canyon National Nature Park |
| 9 | Lechuguilla Cave | New Mexico, USA | Limestone cave | 1900 | Carlsbad Caverns National Park |
| 10 | Sistema del Alto Tejuelo | Cantabria, Spain | Limestone cave network | 1965 | None listed |
Cave systems are ranked by total surveyed passage length in kilometres as listed in Wikipedia's List of longest caves on 18 October 2026, which compiles survey figures from cave survey groups, park services and speleological organizations (for example the Quintana Roo Speleological Survey, CINDAQ and the National Park Service). Length is the combined surveyed passage within one connected cave system. Each figure has its own survey date, so the list is a snapshot of that table on that day: the Shuanghedong figure reflects the 25th international expedition reported in October 2026, while others date from earlier surveys. Exploration is ongoing and lengths will keep growing.
Cave length is the total surveyed passage within a connected cave system. Survey teams measure passages leg by leg with compass, inclinometer and distance readings (today often with laser rangefinders), and the totals are compiled by cave survey groups and national organizations. Because exploration is ongoing, the lengths grow over time as new passages are discovered and surveyed.
A single cave may have one entrance or a few entrances. A cave system is a network of passages that are connected to each other, possibly with multiple entrances. When two caves are found to connect, they are merged into a single system, which is why some entries on this list represent multiple formerly separate caves.
Flooded cave systems in Mexico's Yucatán Peninsula dominate the list because the region's limestone bedrock is highly soluble and the water table is near the surface, allowing extensive underwater passage networks to form. These 'cenote' systems are explored primarily by cave divers, whose systematic surveys have revealed hundreds of kilometres of connected passages.
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