Are you looking for some rare art books? The Solomon R. Guggenheim Museum presents an incredible collection of 200+ books on all sorts of art. The best thing here is that all these books are free.
The collection has everything one can dream of: Wassily Kandinsky’s 1946 treatise, On the Spiritual in Art; Italian metamorphosis and Russian Constructivism; Aztec and Chinese art; catalogs of work by artists to reach the Guggenheim’s Frank Lloyd Wright-designed halls. Can’t get paper versions? The breakdowns of works by Pablo Picasso, Roy Lichtenstein, Dan Flavin, Robert Rauschenberg, Gustav Klimt, Mark Rothko, and more are waiting for you as PDFs and ePubs.