At right, the underground cistern.  The Romans built it as a source of water in case of siege.  Since aesthetics weren't terribly important, scavenged materials such as the Medusa heads were used.

At left, a demonstration (not real) whirling dervish.   I have some pictures of a real dervish (darawish) in Cairo, which I will hopefully post soon. At right, Hagia Sofia.  I took few photos because there are many high quality museum books available.