Mom's has been to Ephesus, when she did "Greece, the Islands, and Turkey." She said it was the neatest thing on that trip. Her current tour is Sicily and Corsica, with stops at Rome and Pompeii, just because they're close, I suppose.
On this trip, Ephesus was my favorite with Pompeii being second. Athens and Corinth would have been third with Mykonos fourth.