Less well known and thus (slightly) less crowded than Versailles, Fontainebleau started life as a hunting lodge and became the favorite residence for many French rulers, and many of them left their distinctive imprint. Francois I., Henri IV., and Napoleon all had an individual entrance built to the palace, and the "School of Fontainebleau" was a model for French and European Renaissance architecture. Many people will imitate the kings and prefer this magnificent complex to Versailles. I wouldn't go this far, but it is certainly very well worth visiting and one of the better daytrips from Paris.