Most of this green area around Frankfurt is left in its natural form, that's why it is a perfect escape from the city.
Wikipedia (German) http://de.wikipedia.org/wiki/Frankfurter_Gr%C3%BCng%C3%BCrtel
More information on Frankfurt's official website http://www.frankfurt.de/sixcms/detail.php?id=3066
Address 60389, Germany
Coordinates 50°9'3.557" N 8°44'7.649" E
