Hacı Ahmet Mosque
Built in 1798, this building superficially resembles a Greek church and as such it might be mistaken for a church-turned-mosque, which are quite usual in western Turkey. However, this was built as a mosque originally, and the catch is that it was the local Greek stonemasons who built the place. It's surrounded by pleasant narrow cobbled alleys which are also worth a look, lined by somewhat dilapidated historical houses.
