The garden you see below this pedestrian bridge is the Reuilly garden in the 12th arrondissement. This bridge is a part of the walkway called "
La Promenade Plantée" which goes across all the 12th arrondissement on 4.5km. It starts from the Bastille Opera house and ends at the Porte de Saint Mandée on the Bois de Vincennes (one of the 2 Paris forest).
This walk has been created on a former railway which was going from Bastille to the east suburb and stopped being used in 1969. The first part of the walk is on an viaduct on the boulevard Daumesnil where the bottom has been renovated to welcome shops and the top has been planted for pedestrian. I will show pictures of this tomorrow.
It is a very nice walk from Bastille to this garden. From there the walk can also be used by bikes up to the Bois de Vincennes.