Iznik is a city with a cultural heritage of 2400 years. Iznik, known as Nicaea in ancient times, has been described by the Christian world as the third "holy city" after Jerusalem and the Vatican.

Iznik, which is 85 km from Bursa, having fertile land and vast historical assets together with a beautiful lake, is known worldwide for its tiles. It was an important city of the Roman, Byzantine, Seljuk, and Ottoman empires.

Two of the Ecumenical Councils were held in Iznik in 4th and 8th centuries AD respectively. As a result of controversies which arose because of doctrinal differences in the Christianty in 320 AD, the Byzantine Emperor Constantine convened the First Council in Nicea in 325. At the Council, attended by 300 bishops, a solution was sought to resolve the controversy over the divinity of Christ. Later, Empress Irene convened the the Seventh Council in 787 AD. At the end of the 19th Ecumenical Council held in the Vatican in 1962, Iznik was declared a "holy city" for Christians.

The city today is an important destination of "Faith Tourism" in Turkey which serves to vary tourism, to impart the image of secular Turkey to the world, and to stress the "tolerance" in Islam towards other religions.

There are several sites to see in Iznik today, such as the Hagia Sophia, which was a Christian church and then converted into a mosque, the city walls and gates, various mosques, and the Archaeological Museum.

Iznik is a member of CittaSlow.