This is the Burmalı Minare Camii (Spiral Minaret Mosque), built between 1237-1247 by the Selcuks.

On the picture: The ‘mihrab’ (prayer niche).

From Wikipedia: Mihrab (Arabic: محراب‎ miḥrāb, pl. محاريب maḥārīb) is a semicircular niche in the wall of a mosque that indicates the direction of the Kaaba in Mecca and hence the direction that Muslims should face when praying. The wall in which a mihrab appears is the ‘qibla wall’.

Correspondent: J.M.Criel, Antwerpen.