Over 200 km in One Source, Over 260 km in Another: The Gypsum Maze of Optymistychna Cave
Optymistychna Cave, underground in Ternopil Oblast in western Ukraine, is a maze-type cave whose passages spread in a net-like pattern along cracks in a gypsum layer. Its length has been given as over 200 km in a 1996 paper, over 240 km in a 2013 government regulation, and over 260 km in a 2022 encyclopedia entry, and even calling it "the world's longest gypsum cave" comes with conditions about what is being compared. This article traces where the figures come from, the nearby caves, and how the site is protected.
Underground near the village of Korolivka in Ternopil Oblast in western Ukraine lies a cave where thin passages spread in a net-like pattern along cracks in a layer of gypsum. This is Optymistychna Cave (Оптимістична, meaning “optimistic”). A 2013 regulation set by Ukraine’s environmental ministry describes this cave as “exceeding 240 km in length” and protects it as a geological natural monument of national importance.
This cave is often introduced as “the world’s longest gypsum cave,” but the length quoted varies by source — 200 km, 236 km, 240 km, 260 km — and even who is comparing it to what when calling it “the longest” is not consistent. This article works through, as of September 2026, how the cave formed, where the length figures come from, nearby gypsum caves, and how the site is protected.
A Maze Formed in a Gypsum Layer
Oleksandr Klimchouk, a Ukrainian researcher of caves and karst (terrain in rock that dissolves easily in water), described the gypsum layers of western Ukraine in a 1996 paper in the journal International Journal of Speleology. A gypsum layer formed in the Miocene Badenian stage runs as a band roughly 300 km long from northwest to southeast, several kilometers to 40-80 km wide, and within it a number of large caves have formed.
According to the paper, the large caves of this region are all “maze-type” caves, where passages form along vertical or steeply angled cracks and then connect widely sideways. A layer of groundwater-bearing limestone lies above the gypsum, topped by a layer of clay, and Klimchouk writes that this clay has protected the caves from being filled with sediment or collapsing.
The 2013 regulation states that Optymistychna’s underground maze lies at a depth of 60-75 meters, within a gypsum layer 20-25 meters thick. The Guinness World Records record page gives the gypsum layer’s thickness as about 20 meters, and the area covered by the cave’s network as about 2 km².
How the Length Has Grown Over Time
A cave’s length is the sum of the passages that cave explorers have surveyed and mapped, one by one. Klimchouk’s paper notes that an “absolute size” such as a cave’s length keeps growing as exploration continues, and that comparing caves against one another is better done using measures such as volume per meter of passage or the density of passages within a given area.
How the Length Figure Has Changed Over Time
| Source | Length | Date of the source |
|---|---|---|
| Klimchouk’s paper (International Journal of Speleology) | Over 200 km (200,000+ m in the table) | 1996 |
| Regulation of Ukraine’s (then) Ministry of Ecology and Natural Resources | Over 240 km | June 10, 2013 |
| Encyclopedia of Modern Ukraine (ЕСУ), volume 24 entry | Over 260 km | 2022 |
| Guinness World Records record page (“Longest gypsum cave”) | 236 km | Undated on the page |
According to the 2013 regulation, the body that uses and is responsible for managing this natural monument is the Lviv civic group “Speleoclub Tsyklop” (спелеоклуб «Циклоп»). The regulation lists exploring and mapping new sections among the natural monument’s ongoing work. The Guinness World Records page gives the cave’s discovery year as 1966. The Encyclopedia of Modern Ukraine (ЕСУ, volume 24, 2022), compiled by an institute of the National Academy of Sciences of Ukraine, also gives 1966, stating that it was found by a group of Lviv cave explorers (M. Savchyn, I. Kachkovsky, I. Maliavina), and that exploration is carried out by the Lviv speleoclubs “Tsyklop” and “Batkivshchyna.”
Who Is Calling It “the World’s Longest Gypsum Cave,” Compared to What?
It is Guinness World Records that has made “longest gypsum cave” the name of the record. The same page also calls this cave the largest cave network in Eurasia. ЕСУ (2022) describes it as the world’s largest gypsum cave by length, and among the largest naturally formed caves of any kind.
Klimchouk’s 1996 paper likewise calls Optymistychna “the longest known gypsum cave, and the second longest cave of any kind,” and states that the top five longest gypsum caves in the world are all in this region. This, however, is a comparison as of 1996. The same paper states that the largest by area and volume is not Optymistychna but Ozerna Cave (area 330,000 m², volume 665,000 m³) and Zolushka Cave (305,000 m², 712,000 m³), with Optymistychna (240,000 m², 500,000 m³) coming next. What “largest” points to changes depending on whether one compares by length or by area/volume.
No official list from a country or public body giving where this cave now ranks among all the world’s caves by length could be found.
Gypsum Caves in the Same Region
Klimchouk’s paper lists 14 large caves exceeding 1 km in length in this region. Of these, 11 are on the Podillia side, north of the Dnister River, and nine, including Optymistychna, lie in a narrow band along the Dnister. Two, Zolushka and Bukovynka, are on the Bukovyna side to the south, near the Prut River.
| Cave | Length (1996) | Region (per the paper) |
|---|---|---|
| Optymistychna | 200,000+ m | Podillia side |
| Ozerna | 117,000 m | Podillia side |
| Zolushka | 92,000 m | Bukovyna side |
| Mlynky | 25,000 m | Podillia side |
| Kryshtaleva | 22,000 m | Podillia side |
| Slavka | 9,100 m | Podillia side |
| Verteba | 7,820 m | Podillia side |
According to the paper, the combined length of these 14 caves in this region came to about 478 km as of 1996. The world’s five longest known gypsum caves were all in this region, and those five together, the paper states, made up well over half of the total known length of gypsum caves worldwide.
A Natural Monument Protected Since 1971
According to the regulation set out in Order No. 251 of Ukraine’s (then) Ministry of Ecology and Natural Resources, dated June 10, 2013, the geological natural monument of national importance “Optymistychna Cave” was created by Directive No. 611-r of the Council of Ministers of the Ukrainian SSR, dated August 2, 1971. ЕСУ dates protection to 1971 and its status as a natural monument of national importance to 1992. A natural monument is one type of protected area in Ukraine’s nature conservation system, alongside national parks and nature reserves (our article on Ukraine’s protected areas).
The same regulation states that the cave lies within the boundaries of the Dnister Canyon National Nature Park, created by Presidential Decree No. 96/2010 on February 3, 2010. Within the monument, fouling the cave’s passages, collecting or destroying mineral or biological formations, and damaging entrance doors or signs are all prohibited, while setting up, in advance-agreed locations and under a set procedure, an underground base for multi-day expedition teams is permitted.
Lists of protected Ukrainian flora and fauna are covered in our article on the Red Book of Ukraine, and the natural environment of the same mountainous region of western Ukraine is covered in our article on Hoverla.
Sources and article record
Sources and references
- Наказ Міністерства екології та природних ресурсів України від 10.06.2013 № 251 «Про затвердження Положення про геологічну пам'ятку природи загальнодержавного значення «Печера «Оптимістична»»1971年8月2日の指令第611-р号、スペレオクラブ・ツィクロプ、国立自然公園「ドニステル峡谷」〈大統領令96/2010〉、深さ60〜75m・厚さ20〜25mの石膏、延長240km超、禁止事項と地下基地. Order approving the regulation on the national-importance geological natural monument "Optymistychna Cave": Directive No. 611-r of August 2, 1971; Speleoclub Tsyklop; the Dnister Canyon National Nature Park (Presidential Decree 96/2010); a gypsum layer at depth 60-75m, thickness 20-25m; length over 240 km; prohibitions and the underground base
Published by Верховна Рада України（法令データベース） · Checked: 2026-09-27 - Alexander Klimchouk「Gypsum karst in the Western Ukraine」International Journal of Speleology 25(3-4), 1996, p. 263-石膏の帯、迷路型の洞窟、14の大洞窟の表、オプティミスティチナは最長の石膏洞窟で全種類で2番目、面積・体積の比較、上位五つ. The gypsum band, maze-type caves, a table of 14 large caves; Optymistychna as the longest gypsum cave and second-longest of any kind; area/volume comparisons; the top five
Published by International Journal of Speleology · Checked: 2026-09-27 - Longest gypsum caveOptymistychna Cave、236km、石膏の層約20m、約2km²、1966年、ユーラシアで最大の洞窟の網の目. Optymistychna Cave, 236 km, gypsum layer about 20m, about 2 km², 1966, the largest cave network in Eurasia
Published by Guinness World Records · Checked: 2026-09-27 - Оптимістична国の重要度の地質の自然記念物、洞窟、ボルシチウ地区. National-importance geological natural monument; the cave; Borshchiv district
Published by Велика українська енциклопедія（国立学術機関「百科事典出版所」） · Checked: 2026-09-27 - Оптимістичнапечера、国の重要度の地質の自然記念物〈1992年から〉、保護は1971年から、延長260km超、石膏洞窟で世界最長、1966年にリヴィウの洞窟探検家のグループが発見、探検はスペレオクラブ「Циклоп」「Батьківщина」。著者 В. П. Коржик、О. І. П'ятківський。第24巻、2022年. National-importance geological natural monument (from 1992), protected since 1971, length over 260 km, the world's longest gypsum cave, discovered 1966 by a group of Lviv cave explorers, explored by speleoclubs "Tsyklop" and "Batkivshchyna." Authors V. P. Korzhyk, O. I. Piatkivsky. Volume 24, 2022
Published by Енциклопедія Сучасної України（ウクライナ国立科学アカデミー百科事典研究所） · Checked: 2026-09-28
If you find an error in this article, please tell us via Corrections. Once we have checked it, we will record in the article what was corrected and why.