Internally displaced Syrian children stand at the entrance of their makeshift shelter that is an underground cave in Om al-Seer, southern Idlib countryside, Syria December 26, 2015. (Photo by Khalil Ashawi/Reuters)
A mother and her daughter paddle during a Stand Up Paddle (SUP) race of the Alpine Lakes Tour, on Europe's biggest underground lake, in St-Leonard, Switzerland, March 10, 2018. SUP is an offshoot of surfing that originated in Hawaii. Unlike traditional surfing where the rider sits until a wave comes, stand up paddle boarders stand on their boards and use a paddle to propel themselves through the water. (Photo by Denis Balibouse/Reuters)
Partially constructed notched burial plots are seen at the construction site of an underground tunnel designated for traditional Jewish burial at the Givat Shaul cemetery, on May 14, 2015, in Jerusalem, Israel. Underground cemetery being built by the Israeli Burial Society in Jerusalem due to a decrease in available land for traditional Jewish burials. (Photo by David Vaaknin/The Washington Post)
The Puerto Princesa Subterranean River National Park is located about 50 kilometres (30 mi) north of the city centre of Puerto Princesa, Palawan, Philippines. The river is also called Puerto Princesa Underground River. The national park is located in the Saint Paul Mountain Range on the northern coast of the island. It is bordered by St. Paul Bay to the north and the Babuyan River to the east. The City Government of Puerto Princesa has managed the National Park since 1992. The park is also known as St. Paul's Subterranean River National Park, or St. Paul Underground River. The entrance to the Subterranean River is a short hike from the town of Sabang.
Stunning silhouettes under European cities reveal the size and splendor of the continent’s urban foundations. Photographer and content-manager Anna Arinova, 28, from Moscow, captured the awe-inspiring labyrinths in Russia and Germany. Here: Regenwurmlager, Poland. The Regenwurmlager is an extensive underground fortification area constructed by Germany in 1920s-1940s, now in western Poland, near the city of Międzyrzecz. (Photo by Anna Arinova/Caters News)
Cappadocia is a historical region in Central Anatolia, largely in Nevşehir Province, in Turkey.
In the time of Herodotus, the Cappadocians were reported as occupying the whole region from Mount Taurus to the vicinity of the Euxine (Black Sea). Cappadocia, in this sense, was bounded in the south by the chain of the Taurus Mountains that separate it from Cilicia, to the east by the upper Euphrates and the Armenian Highland, to the north by Pontus, and to the west by Lycaonia and eastern Galatia.
Željava Air Base, situated on the border between Croatia and Bosnia and Herzegovina under Plješevica Mountain, near the city of Bihać, Bosnia, was the largest underground airport and military air base in the former Yugoslavia, and one of the largest in Europe. (Photo by Thomas Windisch/Exclusivepix Media)