Tivoli - Villa d'Este gardens and Hadrian's Villa are two popular sites here. Its a 40-50 min ride by bus from Rome. We tool the Cotral bus from Ponte Mommelo metro station in Rome to reach here. There are also train options, though direct trains from Termini seemed very limited. Buses leave every 20 mins. The stop at Tivoli is Piazza Garibaldi. Its a 5 min walk from there to Villa d'Este. The fountains and greenery at the garden freshen you up. The climb back up from the garden can be taxing 😬 We didn't make it to Hadrian's villa since this was more of a half day trip for us. If you want to cover both, set aside a day for Tivoli. The return bus fare is 2.80 € per person. Found the visit to the gardens worth the half day trip.