The “Jardin de Plantes” is worth a visit for many reasons – its gardens, a number of museums, a little zoo… I already posted about it several times. If you look for a really peaceful moment I would recommend a visit to what is a bit separated from the rest, the Alpine Garden. (There is an entrance fee only during the weekend.) The “Jardin Alpin”, originally referred to as the “Jardin des Plantes de Montagne” (mountain plants) is as old as the total park – from around 1640, but it has had its present look since 1931.
A special little look on some frogs and some water lilies.
On the way here, you can’t avoid a special look on the Lebanese cedar, planted in 1734… and the “Gloriette de Buffon” from 1787, the oldest metallic installation in Paris. It’s heavily in need of restoration and the park authorities ask for contributions - see here.
Apart from all the more public buildings, there are also some nice old ones, hidden behind trees.