With its fountain, mosque, food preparation building for the poor and the later addition of a madrasa with a library this can be considered as a Külliye.
The Mosque was built in 1506 by Nasrullah Kadi (Judge Nasrullah) during the reign of Ottoman Sultan Beayzid II. With a stone bridge nearby, its fountain in the south of the narthex, with six domes and multiple pillars this was the largest in Kastamonu. With the addition of three more domes in 1746 still remains to be the largest in Kastamonu. Inside the mosque the decorations and religious calligraphy are done by a famous Kastamonu hattat (calligrapher) Ahmet Şevki Effedi.
During the War of Independence, the Turkish National poet Mehmet Akif Ersoy gave an oratory in this Nasrullah Mosque to gather support for the War. He was also the author of Turkish National Anthem and red it here for the very first time after being accepted by the Turkish National Assembly.
When the mosque was build in 1506 it had an absolution fountain with two small pools; however in 1752 they were covered two domes resting on sixteen pillars by a wealthy local. There is also legend among people that once a visitor drinks from these fountains his/her will return to Kastamonu seven times in lifetime or will move in to the town within seven years.