Probably not the Number One reason people come to Paris - to find its oldest tree. Nor to locate the little park in which that tree has lived and thrived for over 400 years, with a lot of support from concrete crutches.
But maybe for its picture-perfect view of Notre-Dame? Definitely worth it as a place to rest the weary feet and munch a sandwich or patisserie and enjoy the view, feeling very far from the crowd.
I discovered this location, Square René Viviani, because one of my classes is in a building adjacent to the park and I usually have an hour break during to which to have lunch there. So I've also discovered that this tiny park has free wifi, along with the plentiful benches, marvelous view, quiet calm AND the oldest tree in Paris.
For the story about the tree, Wikipedia does it better than I would. It's quite something to imagine all the events of Paris history this tree has lived through.
The square is also just across the street from Shakespeare & Co., the well-known English-language bookstore.
Square René Viviani
located on the other side of Pont au Double
(south from Notre-Dame, on the Left Bank)