If anybody wants a tourist-free attraction in Paris, or just a nice spot to relax, I recommend the Canal St. Martin, which runs just northeast of the Gare de l'Est, and mysteriously disappears below ground before it joins the Seine.
On a short stretch of canal, it has an implausible amount of 19th century technology, including high footbridges, locks, and a rotating bridge.
Between Gare de l'Est and the canal there is also a very nice park (whose name I forgot), and in the park-side front of the office building next to the park I spotted this slightly unusual biotope during my stopover in June (en route to Germany):
But by the time I returned to the spot last week, the tree had disappeared and the lifeless order of things had been restored. Also along the canal, this somewhat expressionistic architectural detail: