This is a picture of the tunnel connecting the main concourses at Detroit Metro Airport. I'm going to take a guess and say it's about two football fields long. But the point is actually not to think about how long the tunnel is, or what kind of crappy airport design this implies. Just let the ambient sonic wash and psychedelic colors soothe you while you sprint.
You can enter the belly of the giant cuttlefish known as "Light Tunnel" via this Youtube video.