This is inside the Kurşunlu Camii (leaden mosque), built in 1580/81 and attributed to Mimar Sinan, the greatest Turkish architect. It's nice, but I have seen so many Sinans by now that I was not overly impressed.

This mosque was built in H. 994 (1585-86), according to Ottoman accounting documents related to the building inscription. The draft is certainly from Mimar Sinan and his assistants (that’s important to the people of Kayseri, since Sinan was born near their city). Whether he was personally involved in the building activities is unlikely: at the time he was 97 years old...
The mosque got its name from the lead covering of its central dome.

On the picture: The mihrab and minber, in plain Classical Ottoman style.

Mihrab = 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.’
Minber = a pulpit in the mosque where the imam (prayer leader) stands to deliver sermons.

Correspondent: J.M.Criel, Antwerpen
Sources: ‘Tarihi Kayseri Cami ve Mescidleri’ – Doç. Ilhan Özkeçeci (1997), Wikipedia