Machu Picchu is a mystery, where Incas built an intricate city of stone without wheels, iron tools or beasts of burden.   The temples within are built to catch the sun’s rays, or to observe the stars.  Built around 1450, during the Incan empire, which lasted 100 years until the Spanish conquistadores came with smallpox.   Swallowed by the jungle, it wasn’t “discovered” again until 1911. Now a UNESCO World Heritage Site, questions abound about construction and use.   Sadly, no Inca descendants remain to answer.