This is a Türbe, from the twelfth century, the Kulak Tekke. Some gravestones lying around of an ancient Turkish type, without a trace of the occupants. Inside a monument under some cloth.
The monument.
This is a cenotaph (sarcophagus): an "empty tomb" or a monument erected in honour of a person or group of people whose remains are elsewhere. The word derives from the Greek: κενοτάφιον = kenotaphion (kenos, one meaning being "empty", and taphos, "tomb"). In general, a Turkish türbe has two rooms: an upper room where the cenotaph sarcophagus/sarcophagi were placed to be visited by relatives and followers, and a (cellar) room beneath where the remains of the deceased were buried.
Correspondent: J.M.Criel, Antwerpen.