The Convento Grande de San Ramón Nonato, founded in 1603 in Buenos Aires by Fray Pedro López Valero.

During the British Invasions, this convent played a huge role. It was occupied by defending troops, and during the war with Brazil, it served as a barracks and a hospital. 

Today it houses a restaurant and cafe and even a bookstore. It's a peaceful oasis (cliche but true) in an otherwise busy city center.