Querétaro is Mexico's best representative of the mix of big town, historical heritage and a calm, clean provincial atmosphere.
My suggestion:
Go eat at Biznaga, 17 Manuel Gutierrez Najera, where they have art from the floor to the ceiling. Should you be there on Good Friday you can take part in the strange silent procession.
My review
A magical day at Querétaro begins with a walk along a disused railroad track, then along a river, until you reach the historic center. There are jazz concerts in the Garden of Art or classical music on Constitution square. It very pleasant to wander about the town in the evening, looking at the lit up houses, their flowery balconies, and their old wooden doors, and then realizing that two centuries ago the independence movement began here.