I searched for it, but couldn't find it on here so maybe it has been posted already but here is one of my personal favorites, it's a bit old but still amazing in my opinion:
Casa de Retiro Espiritual designed by the famous Emilio Ambasz. Commonly referred to as the "Book house"
Interesting video which shows it the best:
The official website with a lot of pictures: http://www.casaderetiroespiritual.com/