We left Istanbul in our rental car and drove three days to Gumusluk to visit friends. We stopped twice overnight at small bed and breakfast and during the day if we passed interesting places. One of our stops was Pergamum.

This is reputedly the steepest amphitheatre anywhere in the Roman Empire. You can see the modern town of Bergama below. It seated 10,000 people. This had the steepest seating of any known theater in the ancient world.
Amphitheatres were built on hillsides to maximize the acoustics.

If you ever travel this way - stop! Although some of the most beautiful and intact monuments, such as satans throne is in the Berlin museum, I thought Pergamum was stunning and actually more impressive than Ephesus.