On the picture: The Yıldırım Beyazıt Türbesi (mausoleum) looks like a small mosque, because of the porch (12,80 m wide) adorning its north facade. In fact, it was the first Ottoman ‘türbe’ of this type.
It was erected in 1406, and commissioned by Süleyman Çelebi, a son of Beyazıt I; he was the first ‘Sultan of Rumeli’ (1402-1410) during the Ottoman Civil War (1402-1413) that followed the defeat of Yıldırım Beyazıt against Timurlenk at the Battle of Ankara.

Correspondent: J.M.Criel, Antwerpen.
Sources: ‘Vakıf Abideler ve eski Eserler III’ - Vakıflar Genel Müdürlüğü, Ankara 1983 & Wikipedia.