5 Explore the world’s largest cave
In 1991, a local man discovered a forgotten cave, but couldn’t find a way inside as the drop was so deep. It wasn’t until 2009 that an expedition discovered that it was the largest cave in the world – Hang Son Doong. Stretching more than three miles long and reaching 650 feet, you can now explore the cave with the help of trained guides. Ropes are used to climb into the entrance, as well as up the Great Wall of Vietnam – a calcite wall totalling 90m in height.