In the mountains of Mexico, there is a ritual dance that is so extraordinary that the United Nation's cultural organisation has given it protected status. It takes place at the top of a 30 metre pole, with five dancers in brightly coloured costumes with tassels on. They then leap off, attached only by a long thin cord. It is spectacular. It used to be part of a fertility ceremony, and the people who perform it are called the Voladores of Puebla, …