Meuseo del Prado is different than any other museum. It is likely the most famous one and will no doubt have paintings you recognize from your history textbooks.
True. We stopped by the outside but decided to skip it. It's free in the evenings though, like for the last couple hours before they close. You're also assuming people actually remember pictures from their history books. As a total non-art person, I would recognize maybe 2-3 pieces and I know those ones are not in Madrid.