If you venture deep into the rain forest of Cherrapunji you'll find these amazing examples of natural architecture, root bridges.  Cherrapunji is one of the worlds wettest places covered with rivers and streams.  This is also the home of the Ficus Elastica tree, a species of Indian rubber tree that boasts a very strong root system.   Hundreds of years ago the indigenous people recognized the potential of these rugged roots to help them traverse the treacherous landscape by forming and weaving them into bridges.  

To make these bridges, they would use hollowed out betel nut trunks as channels to prevent the roots from taking root in the soil and guiding them across the river.  Once they reach the other side they take root in the soil and then over years grow to a sturdy root bridge.  The bridges take about 10 to 15 years to grow and there are new ones growing right now.  Some of the bridges in the Cherrapunji are believed to be over 500 years old!

Source: Atlas Obscura via Root Bridges