Nemi, that is also the name of the lake, is worth a visit too. It will make you soak in roman history, thanks to the Roman Ship museum, and will leave you speechless for its breathtaking green-blue view.
Besides villas and history, ancient ruins and astonishing views, Castelli Romani are famous for white wine and the traditional cuisine embodied by Fraschette, typical restaurants formerly used as roman cellars, where you can taste local products, as cheese, porchetta, olives and a glass of good wine.
One of the most famous towns for Fraschette is surely Ariccia where the Hotel Villa Aricia arises.