In 1451 the tomb of Murat II was built. This is it. From a Bursa site I quote: "By leaving open the domed area, where the grave of Murad II. is located, it is ensured that the rain water gets to the grave. It is known that Sultan Murad II. spoke his will saying, ‘’Let the God’s mercy rain directly on my grave either as the brightness of the sun and the moon or Heaven’s rain or dew’’. "

Murad II Kodja (June 1404, Amasya – 3 February 1451, Edirne) (Ottoman Turkish: مراد ثانى Murād-ı sānī, Turkish:II. Murat) was the Sultan of the Ottoman Empire from 1421 to 1451 (except for a period from 1444 to 1446 when his son Mehmed II reigned).

You can see the door to an adjacent room, where the graves of his two eldest sons and his daughter are.

Inside the mausoleum of Murat II (1404-1451).
Two years before he conquered Istanbul Mehmet II, son of Murat II had this tomb built for his father, in accordance with his will. A dome is placed on a tambour with four column capitals from the Byzantine era, a vaulted gallery surrounds the central area. The dome is partly left open at the top, so rain and sunlight can enter, again in accordance with Murat’s wishes. His sarcophagus is very simple.

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