Door within the Templo de Regina Coeli (shrine of the queen of the skies).
My guidebook warned against going south of Mesones in the Centro Historico, but also promised that Regina Coeli was a hidden treasure of religious art. And indeed it is. Completed in 1636, it's a baroque wonder. I could have spent half a day there easily. But a poor woman was trying to mop the floor (slowly moving each long bench to the side all by herself) and I was getting in her way, so I didn't stay long.