I lived in Siena for four months and studied Sienese and Italian history. This cathedral is a rich piece of history and architecture. Its a fully functioning cathedral with the grand walls of a newer cathedral built around it (the Sienese wanted it to be the biggest cathedral in Italy...before everyone died from the Black Plague and couldn't finish it) You do have to pay small fees for different parts of the building, but the main part of the cathedral is free to enter. Defintely a must see!
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