Mark T.
Yelp
I have been to several "squares" in Europe so far, but this is one of my favorites. I think it is my top favorite... for the time being anyway.
The first is the sheer size of this square. I mean it is absolutely massive relative to some other that I have seen. Rather than just being unused space, the square is teeming with people, street performers, horse-drawn carriages, and lots of little shops-on wheels.
These are shops where you can get freshly cooked food (tables are set up), souvenirs of all varieties, and there is even a black-smiths shop that makes little metal trinkets. Even if you don't buy one it is interesting to be able to say you have seen a blacksmith at work.
In the middle, there is a place that used to be an exchange for traders (but now is filled with mostly souvenir shops), and as I understand it, there is a fascinating lower-level museum there (where I have not been).
There is also the St. Mary's Basilica (not been inside, but looks beautiful from pictures), with the bells and the buglers at every hour.
Plenty of restaurants and shops around the perimeter of the square (but they are a bit expensive because of the touristy area). Also plenty of places to go eat and explore just outside the main square.
Overall: An awesome, large, inviting, brightly lit town square which is great to visit at any time of day, evening, or even night.