The 16th-century monastery now serves as a hotel. Still, it is worth stopping by if you're around - the historical features are visible.
Official website http://www.caminoreal.com/oaxaca
Address 300 Calle 5 de Mayo, Oaxaca de Juárez 68000, Mexico
Coordinates 17°3'50.566" N -96°43'21.925" E