Rocca dei Papi is the remains of the old Papal summer residence. At the top of the hill it provides a tremendous view of Lago Bolsena.
Montefiascone Cathedral is one of the earliest structures by Michele Sanmicheli. Dedicated to Saint Margaret (Santa Margherita),
the cathedral was a ruin in 1330 and took three centuries to rebuild.
Subsequently, in 1670, it suffered a serious fire, with repairs taking a
further decade. The interior was elaborately restored in 1893.
More information to be found here, about Montefiascone.
The town piazza is the place to see and be seen on a warm summer evening:
It will take you about 10 minutes drive from Villa Helena.