From the Wikipedia: "Cyzicus (/ˈsɪzɪkəs/; Ancient Greek: Κύζικος Kyzikos; Ottoman Turkish: آیدینجق‎, Aydıncıḳ) was an ancient town of Mysia in Anatolia in the current Balıkesir Province of Turkey. It was located on the shoreward side of the present Kapıdağ Peninsula (the classical Arctonnesus), a tombolo which is said to have originally been an island in the Sea of Marmara only to be connected to the mainland in historic times either by artificial means or an earthquake.

The site of Cyzicus, located on the Erdek and Bandırma roads, is protected by Turkey's Ministry of Culture. "

I tried to take pictures of it, but I found the Zeus temple (in ruins), but failed to find the theatre, amfitheatre and city walls. I have the feeling (having seen others' pictures) hardly anything more might have been seen than a lone chunk of stone.