Denver International is a relatively young airport, having replaced the prior Denver Stapleton. It was designed from the beginning to be big (and expandable). The three existing terminals are parallel and connected by an underground tunnel (similar to Atlanta [ATL], the world’s busiest passenger airport), and the airport left enough room to lengthen these terminals and add more terminals. As a high elevation airport which can get hot in the summer (both of which result in thinner air, and thus less lift for airplane wings), it has one of the longest paved runways in the United States. The airport owns an immense amount of land surrounding it, to avoid getting surrounded by development that would prevent future runway changes.
The tent-roofed main terminal at DEN.
Unfortunately, building such a large airport meant it had to be built a considerable distance from the already-sprawling city of Denver, meaning it can be a bit inconvenient to get to. When traveling to the far southern suburbs of Denver, it often wasn’t much longer of a drive to fly into Colorado Springs (COS) instead.