There's more famous museums, and it doesn't have the most popular paintings for non specialist, but it's just haymaker after haymaker, in every single room. And that's leaving the modern art to the Reina Sofia, a short walk away. (Although I guess keeping late Goya there is kind of cheating, as I'd argue he becomes a pioneer of modern art after the war starts)
Books might require quite a bit of work before you can tell they are eternal masterpieces. Seeing the depths of some forms of music might involve not-so-impressive efforts earlier, just to get to the good parts. The very best paintings in the world, in person, can stop people cold. Large format efforts that demand attention even when you don't consider every single small decision.
The Garden of Earthly Delights used to be stuck in a corner, at the edge of one of the wings of the Prado. As if "oh well, I guess it fits here, near all the medieval art". It counted as an ambush.