I was reading an article earlier on a hidden gem at the Louvre, Napoleon III's apartments. My wife and I visited France a few years ago, and stopped by the Louvre for a few hours. A few things hit me-a lot of the "famous" exhibits were not very busy (Winged Victory over Samathrace, Venus de Milo, etc.), while the Mona Lisa was PACKED...with people facing away, snapping selfies. Kind of amazing, hardly anyone actually looking at it.
The unexpected educational moment I had came at a few different times, looking at Napoleon III's apartments in the Louvre was one. Another came when looking at "Le Petit Palais", with it's 20 ft golden doors, built as a Mother in Laws suite.
Walking in the Jardin des Luxembourg brought the same kind of appreciation. Now a public park, and reduced to ~20 acres from about 80, this was a noblemans walled garden, so they could walk without being mobbed by poor people.
Seeing all this really brought upon an appreciation for the French Revolution, the sheer opulence and extravagance the aristocrats enjoyed compared to the rest of France. Any other "aha!" moments others enjoyed?
Edit: Thought it'd be good to note that I'm not a big fan of the guillotine, sometimes you really just have to see things to understand the history.