Cambodia/Thailand:PreahVihearTemple

A 'Danger' sign warns visitors about a fragile structure within the grounds of the 11th-century Preah Vihear temple. (Paula Bronstein/ Getty Images)

Borders existed before humans appeared on earth -- the high mountains and wide rivers and vast deserts of the world that divide one location from another. Although today's borders are determined by politics, ethnicity, resources and wars, we continue to rely on natural formations to delineatewhere one country ends and another one starts. Whether because of the terrain or because of conflicts between nations, some of these borders have become dangerous boundaries that people cross at their own risk.

Built during the reign of the Khmer Empire in the11thcentury, thePreahVihearTemple is perched on the top of a 525-meter (1,722 ft) cliff in theDângrêkMountains in Cambodia. When it became aUNESCO World Heritage Sitein 2008, UNESCO described it as "an outstanding masterpiece of Khmer architecture, in terms of plan, decoration and relationship to the spectacular landscape environment" that is "particularly well preserved, mainly due to its remote location."

But the temple, which was built to worship the Hindu god Shiva, isn't just known for it's beautiful views and9th-centuryarchitecture -- it also played an important role in the Cambodian civil war and is now the site of a border dispute between Cambodia and Thailand. During the Cambodian war, the temple was the last location to fall to the Khmer Rouge. Although the Khmer Rouge captured Phnom Penh, the capital, in April 1975,PreahVihearTemple didn't fall to the communist forces until late May 1975 because it was so militarily defensible. After the Khmer Rouge gained power in Cambodia, the temple was used as a site to kill Cambodian refugees, either by shooting them or pushing them off the cliffs. Today, the temple is being fought over by the Cambodian and Thai governments. Although the International Court of Justice ruled thatPreahVihearbelonged to Cambodia in 1962, the area surrounding the temple is still disputed.After aborder dispute in 2011left 18 people dead and thousands displaced, the case was reopened in April 2013. Both Thailand and Cambodiamade their arguments to the International Court of Justiceand are waiting to hear a verdict on where the borderlines will be drawn.

NEXT:A jungle trail where people get kidnapped

Panama/Colombia: The Darien Gap

Panama, Darien National Park, trees and clouds in Darien Forest (Kevin Schafer/Getty Images)

The Darien Gap is a 99-mile-long, 31-mile-wide swath of swampland and forest that divides Panama and Colombia. It's also the only gap in the Pan-American Highway, a system of roads that stretches for 30,000 miles through all of North, Central and South America. Although the Darien Gap can be crossed using off-road vehicles, only the bravest -- or most foolhardy -- of adventurers have attempted the crossing. In addition to worrying about venomous snakes, like thefer-de-lanceviper, those trekking across the gap also have to avoid getting captured by the Revolutionary Armed Forces of Columbia (FARC) and being taken hostage or killed. Robert YoungPelton, a travel writer and the author of "The World's Most Dangerous Places," was kidnapped with two other hikers in 2003. After being released,Peltondid an interview withNational Geographic Adventureand said, "It's an absolute pristine jungle but it's got some nasty sections with thorns, wasps, snakes, thieves, criminals, you name it. Everything that's bad for you is there."Peltonadded that although the jungle is beautiful, "it's looked at as a place where you get killed."

NEXT: Dozens of people have died trying to get to the top of this mountainous border

Pakistan/China: K2 Mountain

Pakistan, Karakorum range, Concordia and K2 covered in snow. (Art Wolfe/Getty Images)

Located on the eastern border of Pakistan and the western border of Xinjiang, China, K2 is the second-highest mountain on Earth after Mount Everest. Stretching 8,611 m (28,251 ft.) into the sky, K2 is part of the Karakoram Range and the highest point in Pakistan. Crossing this part of the Pakistan-China border is something even professional mountaineers hesitate to attempt. K2 has one of the highest mortality rates of all mountains, claiming one of every four climbers that attempt to reach the summit. In a story by ABC Nightline, climbers' obstacles are described as "shifting ice, falling rocks, avalanches and sudden storms, [and] high altitude and thinning air." And the trip back down the mountain after reaching the summit is just as dangerous. "Death during descent. This mountain is notorious for this," said climber Eric Meyer in an interview with ABC.Although K2 is the highest mountain along the Pakistan-China border, the rest of the 325-mile boundary isn't much more hospitable. According to an International Boundary Study by the Office of the Geographer in the Bureau of Intelligence and Research, "Human activity and settlement is very sparse and dispersed in the frontier."

NEXT: Hundreds of people perish every year crossing this desert border

US/Mexican Border:SonoranandChihuahuanDeserts

U.S. Border Patrol agents escort a group of undocumented immigrants into custody with helicopter support from the U.S. Office of Air and Marine on May 20, 2013,. near the U.S.-Mexico border in Havana, Texas. (John Moore/Getty Images)

This 1,954-mile border, which encompasses four American and six Mexican states, runs through some of the most dangerous terrain in North America. In the Sonoran and ChihuahuanDeserts, temperatures can fall to the 30s at night and get as high as 118 degrees during the day. Because of stringent U.S. immigration policy and increasing numbers of Border Patrol agents working along the US-Mexican border, immigrants from Mexico are increasingly funneled toward more dangerous locations, such as the harsh deserts south of Arizona and New Mexico.In 2012 alone, 477 immigrants died while attempting to make the crossing, a 27 percent increase in mortality despite the fact that fewer people overall are attempting to enter illegally. According to Ananda Rose, who writes for the New York Times, immigrants are traveling through "remote and perilous stretches of scorching, waterless desert. Fewer migrants may be crossing, but those that do face more treacherous journeys."

NEXT: An ancient part of the Silk Road that has become deadly in modern times

Afghanistan/Pakistan: The Khyber Pass

This mountain pass is one of the oldest in the world -- at one point it was an integral part of the Silk Road. Today it connects Afghanistan and Pakistan, but at an altitude of 3,510 feet, its location in the Spin Ghar and Hindu Kush mountain ranges makes it a dangerous road for much of the year. The name "Hindu Kush" actually translates to "Hindu killer," possibly because the mountains' high elevation and extreme climate make them incredibly dangerous, according to National Geographic. In the past, the pass was used by invaders attacking India from the north and west, including Genghis Khan. Today the narrow road is used by the United States and NATO to provide supplies to American troops in Afghanistan, but it's also used by the militants American troops are fighting against. Because few other roads connect Afghanistan and Pakistan, violence will likely continue to plague the mountain route.

NEXT: The fifth-longest border in the world will soon be entirely blocked off by a huge fence

India/Bangladesh: The Partition of Bengal

The jungles and rivers of this border might look beautiful, but they're part of one of the most dangerous borders in the world. The fifth-longest border is the 2,500-mile boundary between India and Bangladesh. Drawn in 1947, when Bangladesh was still known as "East Pakistan," the poorly demarcated border has caused problems since its creation. Small communities of people are trapped somewhere between India and Bangladesh, and it's estimated that somewhere between 10 and 20 million illegal Bangladeshi immigrants live in India.To prevent more illegal immigrants -- most of whom are Islamic -- from entering the country, India's Border Security Force initiated a shoot-to-kill policy that spares no one. Over the past 10 years, security forces have killed around 1,000 people, mostly Bangladeshis.Additionally, India constructed a 1,790-mile fence between itself and Bangladesh, and by 2014, every crossing point between the two countries will have been blocked off.

NEXT: This desert holds half the sand of the Sahara, despite being 15 times smaller

Saudi Arabia/Yemen: The Empty Quarter

Yemeni men wearing their traditional curved daggers in their belts, walk near the Saudi Arabian border. (Khaled Fazaa/AFP/Getty Images)

Much of the 1,100-mile border between Saudi Arabia and Yemen runs through Rub' al Khali, also know as the Empty Quarter, the largest sand desert in the world. The entire desert is more than 225,000 square miles in size and covers parts of Saudi Arabia, Yemen, Oman, and the United Arab Emirates. According to National Geographic, "It holds roughly half as much sand as the Sahara, which is 15 times the Empty Quarter's size."The harsh desert climate makes it a perilous crossing for those attempting to get from Yemen to Saudi Arabia. "In some ways the border here resembles the one separating the United States from Mexico, another desert barrier between rich and poor nations," writes Robert Worth for the New York Times.Not only do refugees from Africa fleeing war and hunger attempt to cross into Saudi Arabia, but so do smugglers, drug traffickers, and Al Quaeda jihadists. In an effort to keep out terrorists and other undesirable migrants, Saudi Arabia recently announced it would resume construction of a 10-foot-high, 1,100-mile-long fence along the entirety of its border with Yemen.

NEXT: A border separating two countries that are still at war

North Korea/South Korea: The Demilitarized Zone

At the end of the Korean War in 1953, North and South Korea agreed to a cease-fire, creating a permanent Korean Demilitarized Zone that divides the Korean Peninsula in half. Unfortunately, no peace agreement or treaty was signed, so the two sides are technically still at war. Tensions between the two countries remain high to this day, with about 2 million soldiers stationed along the border. In addition to a high, barbed-wire-topped wall, dozens of watchtowers, and land mines, the steep terrain adds to the difficulty of reaching the demilitarized zone.Recently, after months of aggressive rhetoric, North Korea proposed that the two countries reopen a dialogue that has been closed for years so that they can discuss a joint industrial complex in Kaesong that was closed earlier this year. Government representatives from the two countries will meet in the abandoned border village of Panmunjom.

NEXT: Earthquakes and fleeing refugees make this border treacherous

Myanmar/Thailand: The Border at Mae Hong Son Province

A Thai Buddhist monk inspects a fallen stupa of the Chedi Luang pagoda a day after a strong earthquake struck Myanmar near the Thai border, in the Chiang Saen district of Thailand's northern Chiang Rai province on March 25, 2011. (STR/AFP/Getty Images)

Earthquakes, venomous snakes, and the occasional military skirmish are a few of the dangers a traveler might encounter on the border between Thailand and Myanmar. Because the boundary between the two countries is part of the Sagaing fault, periodic earthquakes can cause damage and casualties. In 2011, a magnitude 6.9 quake caused landslides that killed many people in Tachileik, a city on the border of Thailand and Myanmar.There are also a number of Burmese refugees still living on the edge of Thailand, because for years, Myanmar was ruled by a repressive military junta.

NEXT: The third largest desert in the world is the boundary between these two countries

Niger/Chad: The Sahara Desert

Sand dunes of Tazerzait in Tenere part of Sahara desert near Agadez. (Frans Lemmens/Getty Images)

Almost the entire length of the border between Niger and Chad runs through the Sahara Desert, the world's hottest desert and its third largest after Antarctica and the Arctic. The desert covers 3.6 million square miles of northern Africa, and is one of the major travel obstacles of the region. Although the border between these two countries also experiences some turbulence from rebel militia, such as recent Islamist fighters, the real danger is the harsh climate of the desert. Saharan winds can reach hurricane speeds, and half of the desert receives less than an inch of rain each year. With scorching temperatures and few sources of water, the Sahara Desert makes the border between Niger and Chad an extremely dangerous one.

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