This ruined medieval castle overlooks both the Black Sea and the Bosphorus, and offers a great view of the recently opened Yavuz Sultan Selim (Third) Bridge. It originally had eight massive towers in its walls, but little of the original structure has survived. First built by the Byzantines, it was restored and reinforced by the Genoese in the 1300s, and later by the Ottomans. An archaeological excavation is currently underway and as a result access is limited.
It will take you 30 to 50 minutes to walk up to the fortress from the town. Alternatively, taxis wait near the fountain in the town square just east of the ferry dock; they charge around ₺20 for the return trip with 30 minutes waiting time. Restaurants and çay bahçesis (tea gardens) along the walking route serve overpriced food and drink.