I have already made some posts on the different walls that have surrounded the ever bigger Paris.
There is still a rather large number of traces of the Philippe Auguste wall from around 1200. So far I have posted about the largest visible part in the St. Paul area and also about some more discrete ones along the Rue des Francs Bourgeois. I have also referred to one in the small alley, Cour de Commerce St. André and its adjacent court, Cour de Rohan.
Since I made this later post, the place where one of the towers is hidden, a showroom, is under renovation which makes the view through the windows easier. On top of what can be seen is a private home, still inside the tower.
I was told about another trace in an underground parking place, rue Mazarine. I have no car any more, but you can of course enter also as a pedestrian. I wonder how many of the car owners realise that some of the walls are some 700 years old. Paris was on lower grounds when the wall was built and it can be seen as well on the first as the second underground floor.