Caves and tunnels have always been part of human life. We've grown more adept at shaping these underground shelters and passages over the millennia, and today we dig for hundreds of reasons. We excavate to find both literal and cultural treasures, digging mines and unearthing archaeological discoveries. We use caverns for stable storage, for entertainment, and for an effective shelter from natural and man-made disasters. And as the planet's surface becomes ever more crowded, and national borders are closed, tunnels provide pathways for our vehicles and for smugglers of every kind. Collected below are some recent subterranean scenes from around the world.
Tourists visit the Kuha Karuhas pavilion located inside the Phraya Nakhon cave, in the Khao Sam Roi Yot national park, some 300 km south of Bangkok, Thailand, on December 5, 2010. The pavillon was built in 1890 on the occasion of a visit to the cave by King Chulalongkorn, the grand-father of current King Bhumibol Adulyadej.
(Christophe Archambault/AFP/Getty Images)
Participants of the first underground bicycle race compete during the "Mole Race" in a mine under Budapest, Hungary, on Sunday, Feb. 6, 2011. Hundreds participated at the race, pedaling on the 1200 meter (0.75 miles) long track. The more than 30 km (18.6 miles) long mine system were used during centuries to extract stone to build the Hungarian capital.
(AP Photo/Bela Szandelszky)
A visitor walks down the natural entrance at Carlsbad Caverns National Park near Carlsbad, New Mexico, on Dec. 18, 2010. More than 400,000 people visit Carlsbad Caverns each year to get a glimpse of the monumental stalagmites and stalactites, delicate soda straws, translucent draperies and reflective pools that decorate the park's main attraction, the Big Room.
(AP Photo/Susan Montoya Bryan)
Hundreds of cave formations decorate the Big Room at Carlsbad Caverns National Park near Carlsbad, New Mexico, seen on Dec. 18, 2010. Adventurous visitors can opt for several "off-trail" tours guided by park rangers through narrow passage ways, across slick flow stone and down ropes and ladders.
(AP Photo/Susan Montoya Bryan)
Israeli Antiquity Authority archeologist Annete Nagar shows the 2,000-year-old Second Temple period drainage tunnel under Jerusalem's Old City at the west side of the Jewish Wailing Wall on January 25, 2011. Israeli archaeologists have finished work, which started in 2004, on the tunnel that starts at a site near the flashpoint Al-Aqsa mosque compound inside the walls of Jerusalem's Old City, officials said.
(Menahem Kahana/AFP/Getty Images)
Tourists on a banca explore the Puerto Princesa Subterranean River National Park at Kabayugan town, Puerto Princesa, Palawan, western Philippines, on February 13, 2011. The 8.2km (5 miles) long Puerto Princesa Subterranean River National Park was included in the UNESCO List of World Heritage Sites on December 4, 1999 for its ecological universal value and features a limestone formation that contains an underground river that is reputed to be the longest navigable underground river in the world.
Hospital beds are placed in a parking lot set up for the media as an underground emergency hospital, at Rambam Hospital in the northern Israeli city of Haifa May 31, 2011. The lot, equipped with unique filters and air-conditioning systems for protection from biological and chemical warfare, can accommodate 2,000 beds and will be inaugurated in August 2012. According to the hospital's spokesperson, it will be the world's largest underground emergency hospital.
Pakistani soldiers examine the wreckage of a twin truck bombing inside a tunnel in Kohat on January 29, 2011. The attacks took place late night on January 28 in and outside the tunnel which connects the main city of Peshawar in Khyber Pakhtunkhwa province to the city of Kohat.
(A. Majeed/AFP/Getty Images)
Employees pose in a cavern with test drills in a pilot mine which is being tested for potential use as a permanent nuclear waste storage facility, at the salt dome near the northern German village of Gorleben, on July 2, 2010. The mine is some 840 meters deep and 6.5 kilometer long.
Egyptian boys show off rabbits given to them by a Palestinian man (unseen) in an underground tunnel linking the southern Gaza Strip to Egypt on November 21, 2010, as Egyptians and Palestinians transform the network of tunnels that once served as a lifeline for Gaza into its sole export channel.
(Said Khatib/AFP/Getty Images)
Cavers from the Lebanese Association of Speliologic Studies (ALES) descend the path leading to a cave as they go underground to celebrate Christmas with their children and comrades inside a cave in the village of Rweiss nearly at 2,000 meters above sea level in the Lebanese mountains north of Beirut, on December 26, 2010.
(Joseph Eid/AFP/Getty Images)
A driver operates a metro car running through the newly-opened subway line in Beijing on December 30, 2010. Beijing opened five new subway lines to reach the total length of tracks in the city's subway rail at 336 kilometers, which aims at boosting the business growth and social development in the Chinese capital.
(Liu Jin/AFP/Getty Images)
A miner stands in front of a giant drill machine after it broke through at the final section Sedrun-Faido, at the construction site of the NEAT Gotthard Base Tunnel March 23, 2011. The project consists of two parallel single track tunnels, each of a length of 57 km (35 miles).
Pakistani miners emerge from a tunnel during a rescue operation at the coal mine in Sorange district of the insurgency-torn province of Baluchistan, on March 20, 2011. At least seven miners were killed and 41 others trapped underground when explosions triggered a collapse in a coal mine in Pakistan's Baluchistan province, officials said.
(BANARAS KHAN/AFP/Getty Images)
Drums of rum manufactured and matured according to an old recipe stored underground at Santa Teresa establishment, in the village El Consejo del Estado de Aragua, 60km west of Caracas, on April 8, 2011. Venezuela produces more than 32 million liters of rum per year, from which 40 percent is consumed in the country and the rest exported, mainly to Spain and Italy.
(Juan Barreto/AFP/Getty Images)
Faithful walk inside a cave called Minas de Nuestro Senor de Esquipulas, where a legend tells that the "Cristo Negro", or Black Christ appeared, in Esquipulas, Guatemala, on Friday, Jan. 14, 2011. Cristo Negro is the name of a painting of a crucified Jesus in the Basilica of Esquipulas, revered by millions of faithful in Central America.
(AP Photo/Rodrigo Abd)
Twenty-year-old Anil Basnet pushes a coal cart, as he and a fellow worker pull coal out from the rat hole tunnel 300 ft below the surface on April 13, 2011 near the village of Latyrke near Lad Rymbai, in the district of Jaintia Hills, India. The Jaintia hills, located in India's far North East state of Meghalaya, miners descend to great depths on slippery, rickety wooden ladders. Children and adults squeeze into rat hole like tunnels in thousands of privately owned and unregulated mines, extracting coal with their hands or primitive tools and no safety equipment. Workers can earn as much as 150 USD per week or 30,000 Rupees per month.
(Daniel Berehulak/Getty Images)
A small boat quay on a lake at the bottom of Turda salt mine in Turda, Romania (450km northwest of Bucharest) on December 9, 2010. One of the most important salt mines in Transylvania, Salina Turda has been known since ancient times, but was put into operation for underground mining work during the Roman period. The salt mine was mentioned in official documents dating from the middle of the 13th century, when the mine was offered to the Transylvanian Catholic Church leaders.
(Daniel Mihailescu/AFP/Getty Images)
An illegal miner uses a rudimentary pulley to descend into a hole dug in search of gold at a makeshift camp for miners near El Callao in Venezuela's southern Bolivar state, on July 15, 2010. Seven people died in a cave-in at the wildcat gold mine in southern Venezuela, a senior member of the local emergency services told Reuters on August 24.
(Reuters/Carlos Garcia Rawlins)
A subway construction worker, known as a "sandhog" exits the tunnel boring machine in the northbound tunnel of the Second Avenue subway construction project, Thursday, April 7, 2011 in New York. The southbound track has been completed to 65th street and the north bound track is expected to be completed to 65th street by the end of the year. The Second Avenue subway line will run from 125th Street to the Financial District in Lower Manhattan.
(AP Photo/Mary Altaffer)
Curator Joanne Gray puts the finishing touches to the Repeater Station in the subterranean tunnels underneath Dover Castle, which has been restored by English Heritage for a public exhibition on June 3, 2011 in Dover, England. The evacuation of allied soldiers from Dunkirk was masterminded and coordinated from the secret command and control center in the tunnels deep below the castle.
(Matthew Lloyd/Getty Images)
A Mexican soldier looks into a tunnel discovered in Tijuana, on November 25, 2010. According to local media, authorities found a drug smuggler's tunnel linking the northern border city of Tijuana with the United States. The tunnel was fully operational with a system of ventilation and electricity, and rails for the transportation of narcotics.