Engineers, builders, governments, and private parties involved spend months, years, and sometimes decades to design an airport. Yet, with all the planning and effort, some airports can be so frustrating they cause passengers hair-pulling confusion and frustration. Frequent flyers and business travelers learn how to maneuver through the airports they frequent, but the occasional leisure traveler must struggle through poorly designed airports. Unfortunately, many of the world's most confusing airports are hubs to major airlines, so they are difficult to avoid; however, with some preparation, you can mitigate your frustration. Here are the six most confusing airports in the world.

Hartsfield-Jackson International Airport (ATL), Atlanta, Georgia

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For over the last two decades, Hartsfield-Jackson International Airport has been the busiest airport in the world. As a major hub for Delta Airlines and a secondary hub for other major airlines, ATL was the first airport in the world to serve more than 100 million passengers in a year. The confusion of flying in or out of ATL doesn't lie so much in the airport's design, but more in its size. ATL has also been one of the largest airports in the world. It will move down a spot once construction is completed at the new Istanbul Airport in Turkey. Long walks, escalator rides, and tram rides can leave passengers feeling like they are a rat trying to find their way out of a vast maze.

Washington Dulles International Airport (IAD), Dulles, Virginia

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Opened in 1962, Dulles is one of the three major airports to serve the Baltimore and Washington, D.C., area. Those who have ample experience with D.C.'s trains, New York's subways, or light-rail systems in other countries might not find Dulles confusing. Those who fly in and out of Dulles must use the AeroTrain system to travel between the main terminal and concourses. Those who don't have experience with public transportation can find this confusing and feel overwhelmed, especially with a tight connection. This doesn't mean you should avoid Dulles if it works best for your business or leisure travel, but give yourself extra time to navigate their system and plan out connections beforehand.

London Heathrow International Airport (LHR), London, England

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As the busiest airport in the United Kingdom and one of the most active in the world, Heathrow can cause major confusion for passengers traveling to, from, or through the airport. Heathrow is the hub to British Airways, and Virgin Atlantic has a strong presence too. Travelers who fly in and out of Heathrow might not find it as confusing as those who have a stopover or must connect to another flight. The airport's large size doesn't provide time for a leisurely connection, and large crowds make it difficult to navigate. The most confusing thing about Heathrow is its signs. It has so many entertainment venues, shops, pubs, and restaurants that it's difficult to see the signs telling passengers where they need to board.

Los Angeles International Airport (LAX), Los Angeles, California

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Like other airports on this list, LAX's confusion and frustrations are rooted in its size. However, it's not that LAX is too big, but that it's far too small. The airport's awkward, sprawling doughnut-shaped design cannot support the immense traffic which travels to, from, and through the airport. The traffic causes the entrance at LAX to be the most confusing. Los Angeles is notorious for heavy traffic, which includes the airport. Trying to navigate to park, pick up, or drop off among so much traffic makes it confusing to find exactly where you need to be. Those who travel in and out of LAX have learned to deal with its shortcomings. But newcomers and occasional travelers might need to have a drink or two once they get through the obnoxiously long customs, bag-check, and security lines.

Paris Charles De Gaulle International Airport (CDG), Paris, France

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Like LAX, Charles De Gaulle has a circular layout. While the airport can handle the crowds, the tunnel-like narrow corridors found throughout the airport confuse passengers. The layout and tunnels often result in weary travelers waiting in a long line. Even those who find an accurate route throughout Charles De Gaulle will unlikely find a quick pathway to their destination. Passengers connecting through the airport for the first time will likely need to run to make a connection because of the number of wrong turns they will make on the way. To make matters worse, the signs aren't very helpful. Make sure you plan before flying through CDG and allow for extra time if you are connecting.

Frankfurt International Airport (FRA), Frankfurt, Germany

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Frankfurt International Airport is slightly less busy compared to other European airports. But it's counter intuitive signage makes it one of the most confusing airports in the world, mainly because of its massive size. It is Germany's largest and busiest airport, and it also serves as a hub for Lufthansa and Condor Airlines. Following some signs might have you walking in circles to find your gate as you navigate mazes of stairways, tunnels, and escalators. You might even have to walk through a place of business to get to your departure gate.