Looking at it from the window of a plane (or surfing on Google Earth sitting at your PC), Venice appears much greener than it may seem strolling along its streets.
In fact, a surprising number of green spaces dot the city area. Apart from the (few) public parks, most of them are represented by the gardens of ancient religious institutions and palaces, often inaccessible (as the legendary “Garden of Eden” here in Giudecca).
The garden festival, organized every year by the local branch of the Wigwam association, allows everyone to discover some of the those beautiful gardens through a series of guided tours.
The complete program is available at the official website (italian only): http://www.giardini-venezia.it/2015/09/22/festival-dei-giardini-veneziani-2015/