Topkapı Sarayı Palace of sultans from 15th- to 19th-century; housed thousands of imperial servants. Center of the historic district, overlooking city across Sea of Marmara, Golden Horn, and Bosporus. Magnificent treasury of jewels (86-carat Spoonmaker Diamond), elaborately tiled harem chambers and kiosks. Closed Tuesdays. Tip: Eat a substantial breakfast and go early. Harem closes …