Istanbul, also known as Costantinople!
This time unfortunately i can not help you with hostel tips! I have been twice to Istanbul and both times I stayed with my turkish friends! If you are staying in Greece you can either take the bus or train or just an airplane! The first time I went to Istanbul (2006) I went by bus from athens, roundtrip more or less 100euros, the bad thing is that it will take ages to get there, around 22 hours each time, the nice thing is that you will have the opportunity to see beautiful landscape throughout the trip. The second time (2010) I took a plane, much better in just 45 minutes you are there! You can check prices in http://el.aegeanair.com or in http://www.olympicair.com , greek airlines with good deals! When arriving to Ataturk airport Istanbul (IST) you can get a taxi or bus to get down town, the Havas airport bus (10 Turkish lira) will leave you in Taksim square but if you need to go to Sultanahmed you can take the metro or another option is the taxi, for 10 to 1...