Santa Maria delle Grazie does not have wow factor of overwhelming size (i.e. Milan Cathedral). It doesn't merit inclusion for its Byzantine beauty (that's St. Mark's in Venice). A UNESCO-certified church built in the 15th century, this place doesn't make the list for any other reason than that it is the site of the original mural of the Last Supper, the Christian masterwork by Leonardo Da Vinci.
Sure, it's also an attractive old church, but if you've been in Italy more than a day, you've seen close to a billion. One of the great religious works of art in Western culture, The Last Supper is a 15 by 29 foot painting unquestionably worth seeing in person. We suggest joining a tour where your entrance is guaranteed or reserving tickets ahead of time, otherwise you may leave the ticket office with your time having been wasted.
Note:Located on the Piazza Santa Maria delle Grazie to the west of city center.