Dedicated to San Salvador, Ávila Cathedral is truly a cathedral-castle, with battlements and sentry walks incorporated into the structure. It's not just for looks, either - in the 12th century, Bishop Sancho protected the young Alfonso IX until he became king.
Most of the cathedral that can be seen today was built between the 12th and 14th centuries. During this time, the trend moved from Romanesque to Gothic styles, and the transition can be clearly seen in the interior.
The west facade looks quite lopsided - the cathedral remains unfinished and the south tower was never built.