You've probably been to airports many times -- they are so familiar you may not pay much attention to them anymore. But if you go behind the scenes, airports are amazing "mini-cities," providing services to all sorts of people and companies. Air travelers, airlines, private pilots and freight carriers all use airports in completely different ways.

You can get an idea of just how amazing airports are when you consider this: At a typical large airport in the United States, over 100-million people can flow through in just one year. When you consider that the population of the United States is only 300-million or so, that's a pretty startling statistic!

Photo courtesy Denver International Airport
Control tower and terminals at Denver International Airport

In this edition of HowStuffWorks, we will take a look at airports and all of the different things they do for us when we travel!