Just an hour away from Tokyo by bullet train lies a charming mountain town you've probably never heard of. But Karuizawa, a popular summer home location for Tokyo residents looking to escape the city heat, welcomes approximately eight million visitors per year, according to Mari Kashiwagi, secretary of the Karuizawa Tourist Association. For several summers in the 1970s, John Lennon and his family were among those visitors, regularly staying at the Mampei Hotel…