Hidden from view and facing Mount Tuscolo, this mansion was built in the late 16th century for Cardinal Bonanni. In 1730 it underwent extensive renovations thanks to Prince Pietro Piccolomini. It was not given its present name until 1866, when it passed into the hands of Prince Filippo Lancelotti and Princess Borghese Aldobrandini. In the past it welcomed such distinguished guests as Cardinal Cesare Baronio, who wrote his work here Church History, King Charles Emmanuel IV of Savoy and Pope Pius VII, and the writer George Sand, who rented it. The interior is adorned with frescoes by painter Ciro Ferri and boasts a splendid Italian garden, with an ancient nymphaeum from the 15th century.