Mammoth Cave in Kentucky is the longest known cave, with 685.6 km (426 mi) of surveyed passage as of October 2026. These are the 14 longest cave systems, ranked by surveyed length; the figures grow with every expedition.
Pictured: a still from CBS Sunday Morning’s “On the Trail: Mammoth Cave National Park”; Mammoth Cave is #1, with 685.6 km of surveyed passage.
Rank
Cave system
Surveyed length (km)
Country
Region / State
Type
Year of figure
Notes
1
Mammoth Cave System
685.6
United States
Kentucky
Limestone
2022
426 mi after the 2022 survey. Mapped mostly by the Cave Research Foundation, inside Mammoth Cave National Park.
2
Sistema Ox Bel Ha
541.7
Mexico
Quintana Roo
Flooded
2026
Other reports: 524 km (CINDAQ, early 2026); 496.8 km (Quintana Roo Speleological Survey, January 2025).
3
Shuanghedong Cave Network
481.5
China
Guizhou
Limestone
2026
25th international expedition, October 2026; 124 entrances, 912 m deep. It was 409.9 km in 2023.
4
Sistema Sac Actun / Dos Ojos
387.1
Mexico
Quintana Roo
Flooded
n/d
Dos Ojos was joined to Sac Actun in 2018. Guinness gave 371.96 km (QRSS, July 2019); Wikipedia’s article gives 378.6 km underwater.
5
Jewel Cave
354.59
United States
South Dakota
Limestone
2024
NPS: 200 mi in 2018; the park map showed 219.66 mi in February 2024.
6
Wind Cave
270.4
United States
South Dakota
Limestone
2025
NPS: 150 mi in 2019; the park map showed 161.7 mi in March 2022.
7
Clearwater Cave System
268.6
Malaysia
Sarawak
Limestone
2025
In Gunung Mulu National Park; joined to Racer Cave by diving in 2022. Wikipedia’s article gives 265.9 km.
8
Optymistychna Cave
264.5
Ukraine
Ternopil region
Gypsum
2023
The longest gypsum cave. Guinness gave 236 km; surveying has slowed in recent years.
9
Lechuguilla Cave
244.7
United States
New Mexico
Limestone
2022
NPS: over 150 mi (241 km) in 2020. Research and exploration access only.
10
Sistema del Alto Tejuelo
218.5
Spain
Cantabria
Limestone
2026
Spain’s longest. The explorers’ 2025 report gives about 217 km; it was 206 km after the January 2024 connection.
11
Fisher Ridge Cave System
215.9
United States
Kentucky
Limestone
n/d
Wikipedia’s article gives 209.2 km (130 mi, November 2019). Partly within Mammoth Cave National Park.
12
Hölloch
213.2
Switzerland
Schwyz
Limestone
2026
The explorers’ group (AGH) states about 209 km on its site; a 2020 release said 207 km.
13
Siebenhengste-Hohgant-Höhle
164.5
Switzerland
Bern
Limestone
2016
Alpine cave under the Siebenhengste and Hohgant ranges.
14
Schönberg Cave System
159.6
Austria
Totes Gebirge
Limestone
2022
Alpine cave system; Wikipedia cites a 2022 survey summary.
No matching rows.
Read this first: these are surveyed lengths, the total of mapped passage, not straight-line distances, and they change with every expedition. Mammoth Cave, Shuanghedong and Ox Bel Ha each gained dozens of kilometres in a year or two, so ranks can swap, and a cave that has not been surveyed lately (Optymistychna) can fall behind. Lengths are as of 22 October 2026. The rows follow Wikipedia’s List of longest caves (read that day); the top ten were each checked against a second source, mostly the cave’s own authority: the National Park Service for the four American park caves, the Quintana Roo Speleological Survey and Guinness for Sac Actun, press and expedition reports for Ox Bel Ha and Shuanghedong, the Mulu caves project for Clearwater, the Spanish explorers’ club for Alto Tejuelo.[1][2][3] Where sources differ, the notes column shows the other figures. “Year” is the date of the figure or survey it rests on; “n/d” means the source gives no date. Sac Actun’s 387.1 km is the list’s figure, which differs from the 378.6 km underwater length in its own article. Flooded means the passages are mostly underwater and reached by cave divers. Only 14 systems are shown: below 160 km, the surveys are more patchy and sources disagree more, so the table stops there rather than pad it. For deeper caves and show caves see other rankings in Geography & Countries.
The Top 10
#1
Mammoth Cave System — 685.6 km
The longest known cave in the world, in Mammoth Cave National Park, Kentucky. The National Park Service put it at 420 miles in 2021 and, after six more miles were mapped, 426 miles (685.6 km) in 2022. The Cave Research Foundation, a volunteer group, did most of the mapping; a 1972 connection to the Flint Ridge system took the total to 144 miles. It is a dry limestone cave, and it keeps growing with each survey trip. The video is CBS Sunday Morning’s visit with the National Park Service.[1][2]
#2
Sistema Ox Bel Ha — 541.7 km
The longest flooded cave system known, near Tulum on Mexico’s Caribbean coast. Wikipedia lists 541.7 km as of February 2026, while a CINDAQ-sourced report gives 524 km and the Quintana Roo Speleological Survey’s January 2025 update gave 496.8 km. All of the figures point the same way: it is second only to Mammoth Cave and it is still being surveyed. The video is a WION news podcast episode.[1][3]
#3
Shuanghedong Cave Network — 481.5 km
Asia’s longest cave, in Suiyang County, Guizhou. International expeditions have surveyed it since 1988. The surveyed length was 257.4 km before 2023, 409.9 km in 2023, 439.7 km in October 2025, and 481.5 km after the 25th expedition (reported October 2026), with 124 entrances and a depth of 912 m. The jump from 2023 shows how much a single expedition can add. The video is CGTN’s 2023 report, when it was 409.9 km.[1][4]
#4
Sistema Sac Actun / Dos Ojos — 387.1 km
A flooded system near Tulum, Quintana Roo. Divers found the connection between Sac Actun and Dos Ojos in 2018, which briefly made it the longest known underwater cave. Guinness records 371.96 km (231.12 miles) as confirmed by the Quintana Roo Speleological Survey in July 2019; Wikipedia’s list gives 387.1 km, including some dry passage, and its article gives 378.6 km underwater. Ox Bel Ha has since overtaken it. The video is National Geographic’s, from the 2018 discovery.[1][3]
#5
Jewel Cave — 354.59 km
Near Custer, South Dakota, and the second longest cave in the United States. The National Park Service marked 200 miles in December 2018, and a park map showed 219.66 miles in February 2024; the table’s 354.59 km (220.3 mi) is Wikipedia’s figure. It is a limestone cave in Jewel Cave National Monument. No suitable video from an authoritative channel was found, so the icon is shown instead.[1][2]
#6
Wind Cave — 270.4 km
In Wind Cave National Park, South Dakota. The National Park Service reported 150 miles surveyed in 2019 and a map figure of 161.7 miles in 2022; Wikipedia gives 168.0 miles (270.4 km) as of 2025. The park has estimated, from airflow through the entrances, that perhaps only 10% of the cave has been found, and surveyors add about 2 miles a year. No suitable video from an authoritative channel was found, so the icon is shown instead.[1][2]
#7
Clearwater Cave System — 268.6 km
A river cave in Gunung Mulu National Park, Sarawak, a World Heritage Site. Its length grew from 236.8 km in 2020 to about 265.9 km (Wikipedia’s article) after a 2022 diving connection to Racer Cave added about 10 km. The list shows 268.6 km. No suitable video from an authoritative channel was found, so the icon is shown instead.[1][5]
#8
Optymistychna Cave — 264.5 km
The longest gypsum cave in the world, near Korolivka in western Ukraine, and the longest cave in Europe by some counts. Sources disagree on its length: Wikipedia’s list gives 264.5 km, showcaves.com 264.6 km (2023), and Guinness 236 km. Little surveying has been done in recent years. No suitable video from an authoritative channel was found, so the icon is shown instead.[1][5]
#9
Lechuguilla Cave — 244.7 km
In Carlsbad Caverns National Park, New Mexico, and open only to research and exploration. The park’s fact sheet says over 150 miles (241 km) surveyed as of 2020 and 1,612 feet (491 m) deep; Wikipedia gives 244.7 km. Its length was 120 miles in 2007, so most of it was mapped in the last two decades. No suitable video from an authoritative channel was found, so the icon is shown instead.[1][2]
#10
Sistema del Alto Tejuelo — 218.5 km
The longest cave in Spain, in Cantabria. Cavers joined several caves into one system and added 13 km in January 2024, bringing it to about 206 km; the explorers’ 2025 report puts it at about 217 km and Wikipedia’s list at 218.5 km. The video, from the Spanish outlet 20minutos, reports the 206 km connection, so its figure is older than the table’s.[1][5]
US National Park Service: Mammoth Cave adds new miles (420 miles, 2021; the 426 miles of 2022 is from press coverage of the park’s release), Jewel Cave reaches 200 miles, Wind Cave 150 miles and Lechuguilla Cave; the Cave Research Foundation is credited there for the Mammoth Cave survey. The Jewel and Wind map figures (219.66 and 161.7 miles) come from park-store map listings and are secondary.
Videos on YouTube, each ID checked for channel and title: CBS Sunday Morning (Mammoth Cave), WION (Ox Bel Ha), CGTN (Shuanghedong), National Geographic (Sac Actun), 20minutos (Alto Tejuelo). The CGTN and 20minutos clips report earlier lengths than the table.
