You've done Rome. Now do LAZIO. 4 days of day trips or a driving loop: Tivoli (Hadrian's villa + 500 fountains), Bomarzo (Renaissance monsters in stone), Civita di Bagnoregio (the dying city), Sperlonga (Tiberius' grotto on the coast), and the Castelli Romani (Frascati porchetta + lake + papal palace). No tourists. Half the price. Double the surprise.
Each day is a logical geographic loop. Mornings for sights, afternoons for food, evenings for aperitivo.
Day 1: Tivoli. Villa Adriana (morning — 120 hectares, allow 2-3h). Villa d'Este (afternoon — 500 fountains, the Organ Fountain plays at scheduled times). Both UNESCO. Day 2: Bomarzo + Civita. Parco dei Mostri Bomarzo (morning — Renaissance monsters, Hell Mouth, leaning house). Civita di Bagnoregio (afternoon — the dying city, 10 residents, footbridge access only). Both in northern Lazio, 30 min apart. Day 3: Castelli Romani. Frascati (wine tasting + porchetta panino at a fraschetta). Castel Gandolfo (papal summer palace, lake view). Lago di Nemi (volcanic lake, strawberry festival June). Day 4: Sperlonga or Cerveteri. Sperlonga (1.5h south — the white village on the cliff, Tiberius' grotto with the Odysseus sculptures, the beach below). OR Cerveteri (45 min north — Etruscan necropolis, the Banditaccia tombs, 2,600 years of burial architecture).
Best time: April-June, September-October. Book skip-the-line tickets for major attractions.