Fener neighborhood is always remembered with Balat neighborhood, because the area had been an important residential and place of resort by Genoese, Venetians and European traders before 1453 (Istanbul was concurred by the Ottoman Sultan, Fatih Sultan Mehmet). Fener belongs to UNESCO World Heritage list. It is in Fatih district, northwest of the Golden Horn.
After Ottomans conquered Istanbul, due to the Ottoman settlement policies, Ottoman Muslims, Ottoman Armenians and Greeks settled in Fener neighborhood. In 17th century brought Hagios Georgios Church (Church of St. George, Turkish: Aya Yorgi), and it has been the seat of Ecumenical Patriarchate of Constantinople (Turkish: Rum Ortodoks Patrikhanesi).
Fener preserved its character as a Greek neighborhood until the 1950-60s when most of the Greek inhabitants left Istanbul in large numbers due to the political reasons. Then, it became a neighborhood for Turkish people from the Black Sea region. Recently, as a part of Fener and Balat Districts Rehabilitation Programme, which was ran by European Union and Fatih Municipality, the neighborhood has gone through a series of renovations.
Yes, it is definitely a cool neighborhood!! You'll get to see many historical churches, mosques and houses. Don't forget to wear comfortable shoes because you are going to walk on cobblestoned pavement.