What would travel be like if we didn’t have airports? It’s hard to imagine what that would look like exactly, so we have to give thanks to everything that airports do for us—keeping us fed, entertained, relaxed and help pass time by before jumping on another airplane.

But airports are much more than service providers, they are gateways for us to get from one destination to another. And there’s much more to them than we may know, which is why we scoured the Internet for the most interesting airport facts out there. How many of these are you already familiar with?

• The highest air traffic control tower on Earth is located at Suvarnabhumi Airport in Bangkok, Thailand. It measures 434 feet, which is as tall as a 40-story building.

• Before three letter codes became a regulation, airport codes used to be two letters that correlated to the city they were in (i.e. LA for Los Angeles and PD for Portland). After three letters became the custom, airports with two letters added in an “X” to the end, which is why LA is now LAX or PD is PDX.

• San Francisco International Airport (SFO) now has an “airport therapy pig” named LiLou—the first of its kind to help those who have anxiety from traveling. Lilou wears different outfits and does tricks to relax a traveler before they board.

• SFO is also constructed on ball bearings of which there are a total of 267, allowing the airport to move 20 inches in each direction in case of an earthquake.

• Denver International Airport spans 53 square miles, which is bigger than the cities of Miami, which is 36 square miles, San Francisco, which is 47 square miles, or Manhattan, which is 34 square miles.

• When Yugoslavia still existed, the nation invested $6 billion USD to develop an airport underground, known as Željava Air Base. The airport was the biggest underground airport, used during the Yugoslav Wars to prevent airplanes and the airport from being destroyed by nuclear bombs. Although it’s completely abandoned, you can still visit it.

• Tijuana International Airport stands between the US and Mexico border. What makes it unique is that it’s the only airport in the world that and has terminals in two different nations.

• Paro Airport, located in Bhutan, is said to be a difficult airport to land in, and only eight pilots are authorized to land a plane there.

• Juancho E. Yrausquin Airport, found on Saba, a Dutch Caribbean island, is the smallest airport in the world with a runway that’s only 1,056 feet long. The only airline that can currently land there is Windward Islands Airways—all other airlines have to receive a unique approval to land at this little airport.

• Hartsfield–Jackson Atlanta International Airport (ATL) has been recognized as the world’s busiest airport for 20 years. In 2017, 104 million travelers passed through ATL. Following ATL is Beijing Capital International Airport in China at 96 million passengers, and third is Dubai International Airport in the United Arab Emirates at 88 million passengers.

• College Park Airport in Maryland is the oldest airport in the world that continues to operate to this day. Founded in 1909, it was created as a military demonstration site, first used by Wilbur Wright.

• One-third of all the airports in the world are located in the US!