Mosque of Ulmas al-Hajib, Cairo. Flat muqarnas ceiling above the entrance.
(Image has been retouched with local tone mapping (using Paint Shop Pro) to try to provide better view of the muqarnas, but original image has also been uploaded as alternative.)
<a href="//commons.wikimedia.org/wiki/User:R_Prazeres" title="User:R Prazeres">R Prazeres</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>