Sophia Cathedral and the Blue Mosque . Also obligatory to visit are Erebatan-Saray (or "The Failed Palace"), which is an underground water storage; to visit the Topkapi Palace, consisting of several buildings with four courtyards connected by a gate where the Church of St. Irene and the ancient saints and harem of the sultans are of interest; look at Dolmabahce Palace, Galata Tower and Cisterna Basilica with the terrifying head of the Gorgon jellyfish, and from the Galata Tower lookout platform - enjoy the panorama of the historical center of Istanbul . In addition, you can stroll along the ancient city walls that stretch for 22 kilometers through the city districts . And, of course, do not forget to take a ride along the Bosphorus and see the connection of the Black Sea and the Sea of ​​Marmara .