Sinop sits on a headland of Turkey's Black Sea coast, a harbour city with just enough distance from the main inland routes to feel self-contained. It has been Greek, Byzantine, Seljuk, Genoese, Ottoman, and republican, but the story is easiest to read in the walls around the old harbour.
The Sinop Fortress Prison is the reason most travellers should make time for the city. It is grim, memorable, and deeply tied to modern Turkish literature and political history. Around it, the old city walls and harbour, Alaaddin Mosque, and museums make a compact walking day.
Sinop also has the weathered charm of a Black Sea port: fishing boats, tea gardens, summer beach crowds from inland Turkey, and a sea horizon that feels more northern than Mediterranean. It is not polished, and that is part of the point.