Inside the congregation hall of the mosque.
The T-form ground plan of early-Ottoman mosques (the so-called ‘Bursa-type’ mosques) is derived from the late-Seljuk medrese-with-covered-courtyard, with three large iwans (half-open rooms) opening upon a central space. In this mosque, these four rooms are still distinct from each other: their floors are not on the same level.
As the first Ottoman rulers (at least up to their conquest of Constantinople) had strong ties with various Sufi Orders, it is clear that the Bursa-type mosques were designed as multi-functional buildings to meet the needs of these brotherhoods: a place to worship (the ‘mihrab’-room), but also to teach and debate (the ‘iwan’-rooms on the left and right) and even to stay overnight or for longer periods (for this purpose, the Hüdavendigâr Camii’ has at least six middle-sided rooms on its ground floor).

On the picture: The both lateral iwans of the congregation hall, and the central space, whith its marble ‘şadırvan’ (fountain for ritual ablutions). This fountain dates from the 1904 restoration; some sources suggest it was not part of the original 14th century draft. The flight of five steps lead (to the right) into the mihrab area.
Because the mihrab is not visible from within the lateral iwans, their south walls bear a painted version of it. These paintings have been executed in 19th century late-Ottoman ‘Turkish Baroque’ style, influenced by the European (Neo-)Baroque.

Correspondent: J.M.Criel, Antwerpen.
Sources: ‘Vakıf Abideler ve eski Eserler (volume III)’ - Vakıflar Genel Müdürlüğü, Ankara 1983
‘Bursa – Turquie’ – booklet of the Bursa Müzeleri, 1980 & Website of ‘nkfu.com’ .