“Auschwitz. Not long ago. Not far away.,” a traveling exhibition conceived in partnership with more than 20 international museums, including the Auschwitz-Birkenau Museum and New York’s Museum of Jewish Heritage , opens in Boston March 15 at the Castle at Park Plaza. (The Boston Globe is a local sponsor.) With more than 700 artifacts culled from its various partners it tells, piece by piece, some of the personal stories of the camp ’ s many victims through the things they left behind. The exhibition, organized by the Spanish exhibition company Musealia , has been traveling throughout Europe and North America...