Villa Adriana is the largest imperial complex to have survived outside Rome itself, and in summer it becomes a real challenge — little shade, plenty of sun, plenty of tour groups. The solution is simple: bus 4 or 4X from Piazza Garibaldi in the center of Tivoli, arriving just as the gates open. The plastic scale model of the original villa at the entrance gives you a good frame of reference before you set off among the ruins. Plan for three hours, bring water and a hat — shade is scarce.