Considering the Villa Il Tesoro in Siena?
A VT member wrote the following comment about visiting Siena:
Battistero di San Giovanni - open early already by globetrott
Battistero di San Giovanni is certainly worth a visit, as it is just a few steps from the Duomo and it even opens already at 09.00 a.m. - a time , when most of the other museums are still closed, and maybe you come to the Duomo during church-service and will be asked to leave again until the service is over...
..have a look into the Battisterio then !!