Inside a mosque for "whirling dervishes", which has a circular interior, for the dances of the dervishes. In it there are the graves of a number of dervish “sheiks”.

I have been informed by a Kütahya resident the name of the mosque is Dönenler Cami (the mosque of those who rotate).

On the web I found:It was built in the 14th century as the whirling house of the Mevlevihane. This is the first Mevlevihane of Kütahya, and is one of the original examples of early Anatolian Turkish architecture. It has been repaired twice and the semahane and dervish cells remain today. The building, which is used as a mosque today, has an almost square rectangular plan and an octagonal frame.
It is understood from the inscription on the wall of the semahane that it was repaired in 1812 and 1841 AD. The semahane was converted into a mosque by adding a mihrab in a later repair. It is popularly known as Dönenler Mosque.