The Greek island of Santorini, located in the southern Aegean Sea, is home to breathtaking sunsets and cliff side towns with narrow, cobbled streets. It is currently one of the top tourist destinations in the world, hosting millions of visitors each year, with only 15,000 permanent residents. Those permanent residents are easily distinguished from tourists. Just look for the most agile and lean, moving swiftly through the hard-to-navigate, steep terrain. The people of Santorini are in phenomenal shape. Living in a cliff side city means walking up hundreds, if not thousands, of stairs every single day....