Pausilypon Archaeological Park
Atop Posillipo's hill, this small yet magical complex has a 1st-century villa and two amphitheaters; access is though the Grotta di Seiano, a 2,500-foot tunnel cut though the tufa rock over two millennia ago. Guided tours (in Italian, book ahead) are given at 11 weekdays, 10:30 and 12:15 on weekends and holidays. Evening concerts are often held here in the summer.
