Temple of Apollo at Didyma, one of the largest temples in the ancient world. Current home to stray dogs.
The great theater at Pergamon, built into a mountainside, with modern town below. In Roman times, this city had 150,000 people. Off to the left of where I was standing was the great library, rivalling the one at Alexandria. Apparently, the Egyptians weren't too happy about that, so they cut of the supply of papyrus, forcing the Pergamese to develop parchment from animal skin.