Castles & Cathedrals

I've been told that we need to limit the amount of castles and cathedrals we visit on our trip or we'll quickly get sick of them. So far, I've marked a few, but I'd love any suggestions for the must-visit castles and cathedrals of Europe.

Castles:

• Conwy, Wales
• Edinburgh, Scotland
• Chateau de Bonaguil, France
• Neuschwanstein, Bavaria, Germany
• Cheimsee, Austria/Germany border

Cathedrals:

• St Pauls, London
• Westminster Abbey, London
• Salisbury, England
• York Minster, England
• Canterbury, England
• Rouen, France
• Pisa, Italy
• St Peter's, Vatican
• Pantheon, Rome
• Siena, Italy
• Notre Dame, Paris
• Chatres, France (from @philhenley)
• Notre Dame, Paris
• Sagrada Familia, Barcelona, Spain (suggested by my hairdresser)

If I've missed something ridiculously good, comment below.