A little further down the street from the big Madrid must see museums (Prado and Reina Sofia) is the Thyssen-Bornemisza Museum-one of the most important private collections of art (800 pieces-can you imagine owning so much art??!!) that was acquired by Spain in 1993. Housed in a palace built between the 18th and 19th century the building is lovely and the collection ranges from Renaissance to Avante-garde and Pop art. There was a special exhibition of Monet and Abstraction-click on the link for a peek into a fantastic new way of seeing the impressionist master next to Rothko, Pollack, and Twombly. Again, if you're in Madrid, don't miss it!
Hopper (1931) and below Estes (1971)