The tower, the sky and the other buildings were reflected in a shop window across the street (Rue Étienne Marcel). This one almost fooled me. I had to double check to make sure it was a reflection. :-)
By my standards all of the buildings in this reflection are old, but the tower in the middle is very old. It was built in the early 1400s. I've walked passed it several times over the years but I haven't been inside.