To see the Chapel of Notre Dame du Haut in person. This unique and beautiful church located in Ronchamp, France was constructed by Le Corbusier in 1955. I always think of it as the "little church with the Dutch hat" (of course, having no idea if the Dutch have ever worn such a hat but it does remind me of their clogs). I can imagine spending hours in and around this structure because there is so much detail to observe.
Allowing for places of worship inside; framed by randomly placed windows, and outside with the open-air pulpit on the east side, I consider this, of all Le Corbusier's work, to be his most whimsical and fun.
It shows that Modern design does not need to have sharp angles, straight sides, and a sterile feel.