You have to see this to believe what you are seeing. I live quite near and am amazed at this structure every time I drive over or under it. Millau used to be an awful place, full of potential but also full of traffic. The viaduct has taken all the traffic way and Millau is now an extremely pleasant place to start or finish your tour of the Gorge du Tarn.
Whatever you do, no matter how short your time in Millau is, make sure you visit the visitor centre. It is a superb place to learn about the viaduct.