The city center. If you want, you can call the square Piazza Delle Erbe as it was called for hundreds of years, or if you prefer, call it Piazza Trento e Trieste, the name given to it in 1919.
Either way, this is a square you must pass through to get to all the sites, and also because it is simply beautiful and pleasant to sit at one of its cafes.
It is surrounded by important public buildings: the Duomo, the Loggia Dei Merciai — a place where the fabric and wool market stalls stood.
Also, watch the bell tower designed by Leon Battista Alberti and head over to the nearby square, Piazza Del Municipio, where there is an impressive staircase symbolizing the beginning of the Este family’s rule in the city.