The biggest city of Turkey is Istanbul, the city on the straits, connecting two continents. There is even a local idiom which states that Istanbul is spread out upon two continents. Touring Istanbul is an unforgettable adventure. The classic Istanbul favorites include Aya-Sofiya Museum, an early Christian Church which was built by the Emperor Justinian; Blue Mosque; Topkapi Palace, which was used by the Ottoman Sultans from the 15th to 19th centuries. Other places of interest include Hippodrome with Obelisk of Theodosius, streets of Old Istanbul and the hidden underground Theodosian Cistern. It is really worth to make a daytrip along the Bosphorus, the strait that separates Europe from Asia.