Pergamon's Acropolis is one of Turkey's great ancient sites. The city was built on a steep hill, so the ruins unfold vertically: theatre seats dropping down the slope, temple terraces, old fortifications, and broad views over Bergama and the surrounding plain.
The famous Altar of Zeus is mostly in Berlin, and some remains are fragmentary, but the site still has force. Walk it slowly, because the shape of the hill is as important as any single ruin.