The answer is: the Mosque-Cathedral of Cordoba (Spain).
In 784, Abd al-Rahman I ordered the transformation of the old and small Visigoth church standing in the same location, into a Great Mosque. Afterwards, subsequent Muslim rulers continued expanding it. It was transformed into a Catholic Church after the Christians took over the city in 1236, during the period known as Reconquista. Anyway, the Muslim influence is still visible. It is mixed with the posterior Christian elements, and such mixture provides great beauty to the temple.