I studied Art History in high school, using Gardners "Art Through the Ages," an iconic Art History survey book. 20+ years ago it cost ~$80, and weighed a ton.
Much of the same content is now available for free at Smarthistory, a non-profit. Amazingly well-done, I quickly got sucked in.
This is not good news for the textbook market. Smarthistory shows that non-profit / open source entrants can start to collapse the existing "value chain." Its going to be an interesting next decade in the textbook market.
Below is Piet Mondrian's Broadway Boogie Woogie (MOMA, 1942). Smarthistory has some great background / historical context on the painting. Clearly a man very much in love with his adopted home, NYC. I love the elemental (yet sophisticated) vitality.