Thanks to the New Liturgical Movement: http://www.newliturgicalmovement.org/
Here, for example, is the Iglesia del Cristo de la Luz in Toledo, which is actually a former mosque built in the year 999, later converted into a Christian church. It was after this that the apse was added to the original building.
As well, I wished to share with readers some images from the remains of the 7th-8th century visigothic Ermita de Santa María (Quintanilla de las Viñas).
First, to give some context here is what we are seeing:
Here then are some details of this fascinating structure: