Istanbul Fethiye Museum, formerly known as Pammakaristos Church, is a fascinating example of Byzantine architecture located in the heart of Istanbul. Built in the 11th century, the church was converted into a mosque after the Ottoman conquest of Constantinople in 1453, and then into a museum in 1951. The museum boasts a stunning collection of mosaics and frescoes, as well as artifacts from the Ottoman period. Visitors can marvel at the intricate designs of the dome and apse, and admire the intricate decoration of the interior.