Can you imagine walking three kilometers across a city without stopping once at a traffic light ? Today , cities are very crowded and often there is no space for a park but some cities have found a great solution – a park in the sky . Long ago , cities built train tracks 10 meters above the city to remove dangerous train tracks from city streets . This made the streets safer , but millions of people suffered because the trains were noisy and dirty . Because of this , many cities closed these train routes , leaving lots of space high above the sidewalk . Today , this space has become a new kind of park . One of these parks is the Promenade Plantée . It was a 5-kilometer train track across eastern Paris , 10 meters above the sidewalk . In 1969 it was closed . For 20 years , the train tracks remained unused , but not forgotten . Then , in 1980 , architects Jacques Vergely and Philippe Mathieux had a brilliant idea . They thought the track could be turned into a nature spot in the middle o...  אל הספר