"Those small, cool, quiet Mona Lisa smiles"
One of the most famous paintings in the world, the Mona Lisa was painted in 1503-4 by Renaissance genius Leonardo da Vinci.  The enigmatic smile of the subject, Lisa del Giocondo, has been admired for centuries; at first glance, her expression could almost seem neutral, but the longer one looks, the clearer the smile appears.  The painting currently belongs to the French Government and displayed in the Louvre in Paris.  Frustratingly, viewers are generally unable to gaze at the painting for more than a few seconds, due to the practice of filing crowds of admirers past it; an estimated 6 million people view it each year.  It is displayed inside bulletproof glass due to several vandalism attempts, and is a smaller in size than many people expect.  It is currently insured in the region of $700 million.    

Official website of the Louvre Museum