Complex sentence: The Cathedral of Ávila in the south of Old Castile, Spain, was planned as a cathedral-fortress, its apse being one of the turrets of the city walls.
Split into simpler sentences: The Cathedral of Ávila is a church in Ávila in the south of Old Castile, Spain. It was planned as a cathedral-fortress, its apse being one of the turrets of the city walls.