Villa Adriana (aka Hadrian's Villa in English) reminds me a bit of Ostia Antica, except that this one has ruins of a large private villa rather than of an actual public town. It's a nice place to walk around and leisurely rest on the benches. And in my opinion, the pools/fountains are the nicest part.
If you're visiting all 3 villas in Tivoli (Villa Adriana, Villa d'Este and Villa Gregoriana), note that this is the largest of the three and it's the one that's the most open and exposed. So it's best to go in early day or late afternoon when the sun is less strong.
Note that they don't have any restaurant to buy food/water, so bring your own if you plan to stay the full day (which is easy to do since it's so large)!
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