If there's one park in Paris that has it all, it must be Jardin des Plantes. Here you can find a mini forest, a gorgeous park with beautiful flowers during the springtime, a zoo (yes, I'm serious), a little maze and a fantastic museum that you really shouldn't miss during your visit here.
I recently took an early morning walk around here and even though it was super cold there was a crazy amount of morning runners out and about. Now when I think about it I was probably the only person not running... I guess I have to get up and join them next week!