In the depths of northeastern India, in one of the wettest places on earth, some bridges are grown from the roots of a rubber tree, the Khasis people of Cherapunjee use betel-tree trunks, sliced down the middle and hollowed out, to create "root-guidance systems." When they reach the other side of the river, they're allowed to take root in the soil. Given enough time a sturdy, living bridge is produced.
The root bridges, some of which are over a hundred feet long, take ten to fifteen years to become fully functional, but they're extraordinarily strong. Some can support the weight of 50 or more people at once.
One of the most unique root structures of Cherrapunjee is known as the "Umshiang Double-Decker Root Bridge."
It consists of two bridges stacked one over the other.
Because the bridges are alive and still growing, they actually gain strength over time, and some of the ancient root bridges are used daily by the people of the villages around Cherrapunjee may be well over 500 years old.