What is the shortest international border in the world, measuring only 85 meters (279 feet)? This border separates two countries located on the island of Borneo. One country is Brunei, a small oil-rich sultanate. The other is Indonesia. The border is so short that you could walk across it in about one minute. The border is not a simple straight line – it follows a creek and then cuts across land. Brunei is divided into two separate parts by a panhandle of Malaysia; the shorter border is between Brunei and Indonesia's Kalimantan province. The border was established during colonial times when the British and Dutch divided Borneo between their spheres of influence. Despite its shortness, the border is patrolled and has a formal crossing point. By comparison, the shortest border between two major countries is between Spain and Morocco at the Peñón de Vélez de la Gomera (85 meters as well, but that's a Spanish enclave in Morocco).

What is the official name of the heavily fortified border separating North Korea and South Korea? Despite its name, this 250-kilometer (160-mile) long and 4-kilometer (2.5-mile) wide buffer zone is one of the most militarized borders on Earth. It contains an estimated 2 million landmines, barbed wire fences, tank traps, and over one million troops on both sides. The name "Demilitarized Zone" is a misnomer because it is actually the most heavily armed border in the world. The DMZ was established by the Korean Armistice Agreement in 1953 at the end of the Korean War. The Joint Security Area (JSA) at Panmunjom is the only place where forces from both sides stand face-to-face. The DMZ has inadvertently become a wildlife sanctuary because humans have been excluded for 70 years – it is home to endangered species like the Korean tiger and red-crowned crane.

Which international border is crossed the most times annually, with over 300 million crossings? This border separates two countries with a long history of close economic and cultural ties. The border is 1,954 kilometers (1,214 miles) long – the longest border between two countries in North America. Approximately 400,000 people cross it daily for work, shopping, tourism, or family visits. The border includes 120 official crossing points ranging from major ports to small rural crossings. At the busiest crossing (between San Diego and Tijuana), over 70,000 vehicles and 110,000 people cross each day. The border has been heavily fortified in recent years with walls, drones, surveillance cameras, and over 20,000 border patrol agents. Despite the security, it remains the most crossed border because of the massive economic integration between the two countries. One country is the world's largest economy; the other is its third-largest trading partner.

Which international border is famous for being the longest undefended border in the world, with no military troops stationed along its 8,891 kilometers (5,525 miles)? This border stretches across forests, lakes, prairies, and mountains, including the Great Lakes and the Rocky Mountains. It has been peaceful since 1815, making it one of the oldest continuous peacetime borders. The border is so trusting that the International Peace Garden straddles the boundary, and the Haskell Free Library and Opera House (in Vermont and Quebec) has its stage in one country and its seats in the other. The border includes 119 official land crossings. The two countries share the world's largest freshwater lake system and the St. Lawrence Seaway. The border was established primarily by the Treaty of Oregon (1846) and the Webster-Ashburton Treaty (1842). It is often cited as an example of successful conflict resolution between former enemies.

Which border is the longest continuous international border between just two countries, measuring 8,891 kilometers (5,525 miles)? This border is actually tied with another border for the title of longest. The border between the USA and Canada is 8,891 km. However, the border between Kazakhstan and Russia is 7,644 km, which is shorter. The Argentina-Chile border is 5,308 km. So the Canada-USA border is the longest. However, it's important to note that the Canada-USA border includes the border between Canada and the continental US plus the border between Canada and Alaska (which is separate). The Alaska-Canada border alone is 2,475 km. The border is so long that it passes through four of the five Great Lakes (excluding Lake Michigan entirely within US). The border includes the longest international water boundary (shared lakes and rivers).

Which two countries each border 14 other countries, the most of any nations in the world? One country is the world's largest by land area (Russia). It borders Norway, Finland, Estonia, Latvia, Lithuania, Poland, Belarus, Ukraine, Georgia, Azerbaijan, Kazakhstan, China, Mongolia, and North Korea. However, note that the border with Lithuania and Poland is via the Kaliningrad exclave. The other country is the world's most populous (China). It borders North Korea, Russia, Mongolia, Kazakhstan, Kyrgyzstan, Tajikistan, Afghanistan, Pakistan, India, Nepal, Bhutan, Myanmar, Laos, and Vietnam. Both countries are located primarily in Asia. Russia also borders several breakaway states that are not universally recognized. The third-highest is Brazil (borders 10 countries) and the fourth is Germany (borders 9 countries).

Where can you find an international border that runs through a library, with the stage in one country and the seats in another? This unique border crossing is located in the village of Derby Line, Vermont (USA) and Stanstead, Quebec (Canada). The Haskell Free Library and Opera House was intentionally built directly on the USA-Canada border in 1904. The border line runs through the floor of the reading room and the opera house. The stage is in Canada, but most of the seats are in the USA. Visitors can enter from either country, but they cannot cross the border inside the building without reporting to customs. The library has two entrances – one in each country. It is the only library in the world with an international border running through it. The library was donated by Martha Stewart Haskell and Colonel Horace Haskell as a gift to both communities. There is a black line marking the border on the floor.

Which agreement allows passport-free travel between 27 European countries, effectively making their internal borders invisible? This agreement was signed in 1985 in a small town in Luxembourg. It initially had 5 signatories (France, Germany, Belgium, Netherlands, Luxembourg) and has grown to 27 countries, including 23 EU members plus Iceland, Norway, Switzerland, and Liechtenstein. Within the Schengen Area, there are no border checks between member countries – you can drive from Portugal to Poland without showing a passport. The area has a population of over 420 million people. External borders are jointly controlled. The UK and Ireland are not members (they have a Common Travel Area). Bulgaria and Romania became partial members in 2024, with land border checks expected to be removed. The agreement is named after the town of Schengen, Luxembourg. Some countries have temporarily reinstated border checks due to security concerns or refugee crises.

Between which two countries can you stand on a beach and see tomorrow on one side and yesterday on the other? This unique border is created by the International Date Line running through the Pacific Ocean. The islands of the Diomede Islands are only 3.8 kilometers (2.4 miles) apart. Big Diomede (Russia) is on the west side of the Date Line (UTC+12). Little Diomede (USA, Alaska) is on the east side (UTC-9). Because of the Date Line, the time difference between them is 21 hours during winter and 20 hours during summer. When it is 10 AM Monday on Little Diomede (USA), it is 7 AM Tuesday on Big Diomede (Russia). So the Russian island is almost a full day ahead. This is why the islands are nicknamed "Tomorrow Island" (Russia) and "Yesterday Island" (USA). The islands are separated by the Bering Strait, which is frozen in winter, allowing (illegal) walking between the countries.

Which border has the greatest elevation change, from the Pacific coast to the peaks of the Andes Mountains (6,900 meters / 22,600 feet)? This South American border runs for 5,308 kilometers (3,300 miles) from north to south along the spine of the Andes. It separates two countries that have very different geographies – one is on the western side of the mountains (along the Pacific Ocean), and the other is on the eastern side (along the Atlantic Ocean). The border includes 26 passes (called "pasos" in Spanish) at elevations over 4,000 meters, plus the highest international border crossing in the world (Paso de la Cumbre at 4,730 m / 15,520 ft). The border features active volcanoes, including Ojos del Salado (6,893 m), the world's highest active volcano. The border was defined by the Boundary Treaty of 1881 and was the subject of several territorial disputes, including a dispute over the Beagle Channel that almost led to war in 1978.