Covering 600 square miles of the northernmost coast of Vietnam's South China Sea coast, UNESCO World Heritage Site Halong Bay (also spelled Ha Long) has become one of this country's most popular tourist attractions thanks to its 1,600 dramatic limestone islands, caves, and floating fishing villages. The tourism boom has included scores of cruises in midsize ships ranging from overnighters to several days in length. What is it like to experience one of these?  keep reading