Picasso Museum/Museu Picasso
My sense is that this Museum has a rep. as an over-priced tourist trap, but I thought it was maybe the best "single artist/subject" Museum I've ever seen because it documents the Artistic growth of one of the most significant/popular Artists of the 19th, 20th and 21st century: Pablo Picasso.
Pablo Picasso has been so thoroughly canonized by the Artistic/Industrial Complex that is hard to even think of him as anything other then a Greek God of studio art, but Museu Picasso has assembled a collection of materials that can thoroughly refute that conception of Pablo Picasso and his Art.
Museu Picasso starts with Picasso's juvenilla, and guides us through his (extensive) formal education which took him to Madrid where has "dropped out" of the French Academy inspired "official" Artistic education, back to Barcelona, where he soaked in the influences of the proto-Modern Catalan "avant garde" and then to Paris, where he was heavily, and obviously influenced by the work of Henri Toulouse-Latrec.
Throughout the galleries the visitor is able to gather a firm sense of the various stages of Picasso's Artistic evolution, from talented youngster encouraged by a family with means, to sceptical but avid student who is willing to "work the system," to shiftless Bohemian trying to "make a name" and hanging out with fellow Artists in Barcelona, to Paris, where he meets with an Audience that is "ready" for the Artistic break-through of Cubism.