Museo Nacional del Prado

A massive museum in Madrid, steps away from the expansive Parque de El Retiro. Lots of important Spanish paintings alongside Medival, Renaissance, and Baroque works. My favorites include The 3rd of May 1808 in Madrid, Goya's Black Paintings, and Queen Joanna the Mad. They're very strict about taking photos in the museum; most of the staff I saw were polite about it but I saw a few who definitely were not. Overall a great museum.