Catedral de Ávila

You're standing at Ávila Cathedral, officially the Cathedral of the Saviour. Take a good look at it. It feels less like a church and more like a castle. That's no accident. It was planned as a cathedral and a fortress at the same time. The rounded east end, the apse, is actually built into the city walls, where it forms one of the towers. This church quite literally helped defend the town.