Madrid, Spain: Museo Nacional del Prado

If you only have time to visit one art museum in Spain, then the Prado is the one to see. It's considered one of the great museums of the world, and a clear leader when it comes to Spanish art. You can almost trip over the masterpieces while taking a look around.

The collection ranges from the 1100s all the way to early in the 20th century; more modern works can be found elsewhere in the city. Some of the artists represented here are Goya, Bosch, El Greco, Rubens and Velazquez. I won't bother to do into detail, but needless to say there's a lot to see here on the three floors of the main museum. There are a few other quality museums in the immediate area, so you can certainly spend a day within that part of town and see a great deal.

The Prado has made an interesting decision when it comes to visitors. Photos aren't allowed of the works. That forces people to actually look at the pieces rather than worry about getting a selfie. It does have a civilizing effect on the crowds.