By 1924 Le Corbusier was 36 years old and had built very little. Yet, he had already designed a "Contemporary city of three million inhabitants" (that was roughly the population of Paris at the time) and his "Plan Voisin", a complete tabula-rasa transformation of the historic center of Paris. For the 1925 Exposition International des Arts Décoratives he set out to build, literally, a house for his vision of the city. On a tight structural grid--the "ossature domino" that would accompany him for his whole life--and within an uncompromisingly compact rectangular plan, Le Corbusier crams together two completely different spaces, one an exhibition hall of curving walls with large dioramas illustrating his urban plans, and the other a full-scale furnished dwelling of the new city, complete with a tree piercing through its roof-terrace.
The Pavillon de l'Esprit Nouveau is well known, but I'm not sure people realize what an extraordinarily bizarre project it is. The two portions of the building are brutally different from each other, in form, in scale, in program, and in every other conceivable way, but rather than trying to articulate them, Le Corbusier simply attaches them side by side to then develop an elaborate "promenade architecturale" coming and going from one side to the other. It is as if he had designed the building equivalent of a mermaid or a centaur.