Iznik is the modern Turkish town on the site of ancient Nicaea, a name that still carries real weight. Two early Christian councils met here, Byzantine and Ottoman layers sit almost on top of each other, and the old town is still held inside a Roman street plan and long runs of city wall.
The centre is compact and easy to walk. Hagia Sophia, Green Mosque, the city gates, and the lakefront can all fit into a single day, with time left to look at tile workshops. Iznik tiles were among the great decorative arts of the Ottoman world, and the town has revived the craft after centuries of decline.
Iznik is not polished like a museum town. Some ruins are fragmentary, some monuments are closed or half-restored, and ordinary streets cut through very old ground. That is part of the appeal. You come for layers: Roman gates, Byzantine basilicas, early Ottoman mosques, lake light, and the blue-green flash of tilework.