Yılanlı Kilise (the Snake Church) is a simple barrel-vaulted church with a low ceiling and long nave. It is named for the fresco of Saints Theodore and St George slaying the dragon (or snake as depicted in the fresco). The church also has a fresco of Emperor Constantine and his mother Helena depicted holding the True Cross. Legend has it that she discovered the cross upon which Jesus was crucified after seeing it in a dream, and that a piece of the cross is still buried in the foundations of the Hagia Sophia in Istanbul. Other sections of the cross are in the Church of the Holy Sepulchre and in St. Peter's in Rome. Another interesting portrait is the one of Saint Onuphrius on the upper wall to the right of the entrance. The saint lived the life of a hermit in the Egyptian desert near Thebes, Egypt and is usually depicted with a long gray beard and wearing only a fig leaf.
Source: Churches of Göreme - Wikipedia