Istanbul  is Turkey’s most populous city, and its cultural and financial center. Located on both sides of the Bosphorus, the narrow strait between the Black Sea and the Marmara Sea, Istanbul bridges Asia and Europe both physically and culturally. Istanbul’s population is estimated to be 16 millions.So istanbul is the biggest city in europe…

and there are a lot of beatiful places to see.

Sultanahmet is the Istanbul of postcards and history. This small peninsula has witnessed more history than most countries. If you see only one building while here, make it the Haghia Sophia (‘Holy Wisdom’, Sultanahmet Square, 522 1750). After close to 1,000 years as a church and then 500 years as chief mosque of the Ottoman Empire, it’s now revered by Christians and Muslims alike. Directly north of Haghia Sophia is the imperial enclave of Topkapı Palace (Bab-ı Hümayün Caddesi, Gülhane, 512 0480, closed Tue). The palace was the hub of Ottoman power for more than three centuries, and for lavish decor and exquisite setting, it is a must-see. Read more »

Turkey is fantastic country.

Also Istanbul is very big city and alot of places to visiting.
For exaple Sultanahmed Mosque,Topkapi Palace,Taksim Square,Galata Tower etc….

And in istanbul hotels are cheap and clear.