Nicknamed dancing bridges, the flexible and unstable rope bridges owe their french name ponts de singe to the agility required to cross them, especially in windy weather. These suspension bridges, which can only be taken on foot, make it possible to cross valleys or rivers where one doesn't want or cannot build hard infrastructure. This is the case of Cœur Bouliki, a natural site considered the green lung of Martinique, where a 78 ft (24 m) long rope bridge (photo) has been installed to cross the Rivière Blanche.