All these pictures are from the monumental grave chamber of Eyüp, which is covered with Iznik tiles of the best quality. The grave proper is in a room that one can look into through elaborate grating. In the room where the believers gather there is a showcase with what must be a footprint of the prophet, I distinctly think it used to be in the Topkapı museum. Here it is much more in its proper place.
For all I know the piece of stone in the centre foreground is venerated as a footprint of the Prophet.