We’re going high up into the Peruvian Andes in South America, more than 2,000 metres above sea level, to the ancient lost city of Machu Picchu, one of the world’s most spectacular places. It was named one of the seven wonders of the modern world in 2007. But it’s also one of the most mysterious. Who really built this awesome citadel and what it was used for has puzzled people for a long time... Mysteries of Science is a multi-award-winning, fortnightly podcast created by The Week Junior's Science+Nature magazine and Fun Kids. Tap follow or subscribe wherever you're listening to this to make sure you never miss an episode. Get three copies of The Week Junior's Science+Nature magazine for just £5. sciencenature.theweekjunior.co.uk/podcast is the place to claim yours. See omnystudio.com/listener for privacy information.