The place in Paris I love most must be the Palais de Tokyo. It was built for the '1937 Exposition internationale des arts et des techniques dans la vie moderne', which drew over 34 million visitors during its five month run. Today, the exhibition is remembered mostly for the fact that the bombastic Nazi-German and Sovjet-Russian pavillions where built opposite each other, facing each other across the Ponte d'Iena in an "I'll meet you in Poland baby" arrangement. Also, it is remembered for the exhibition of Picasso's Guernica in the pavilion of the war-torn Spanish Republic. (designed by architect José Luis Sert in collaboration with Juan Miro, Alexander Calder and Picasso).
Here and here are some links to sites with 1937 photographs of buildings and pavillions for the Exposition Internationale.
The Palais de Tokyo was designed by architects Dondel, Aubert, Viard and Dastugue. The monumental architecture presents two autonomous buildings, seperated by a large terrace but held together by a huge portico. Nowadays, the building is used minotaurically: partly as an official museum of modern art (with some wonderful cubist and surrealist work) and partly as a temporary autonomous zone for contemporary artists and skaters. The building itself reflects it's minotauric use: built in the sternly martial building style of the nineteenthirties, it is now covered in a caleidoscopic explosion of colours by many graffiti artists.