Meaning literally 'descending dragon bay', Ha Long Bay in Vietnam is a UNESCO World Heritage site located in the Quang Linh Province. The Bay has an area around 1,553 km2, including 1,960-2,000 islets, most of which are limestone. The limestone in this bay has gone through 500 million years of formation in different conditions and environments, and as a result has created an enormously rich biodiversity, and is home to 14 endemic floral species, and 60 endemic faunal species. A truly staggering place.
EcoFriendlyVietnam.com offer reams of information on the fascinating geological history of Ha Long Bay that has caused the beauty of its current state, and they also offer and recommend tours of the area. Try, for instance, the Sail Boat Tours of Karsts landscapes created by a complex chain of millions of years of geological movement. And Cat Ba Island, formerly named "The Pearl Island", is the largest island in the Ha Long Bay vicinity.
AudleyTravel.com also offer similar boat tours, though these will interest the ecotourist by way of observing the local Vietnamese daily lifestyle. Cruising the calm waters through the limestone islets, you will see Vietnamese life at its most unspoiled and traditional, with families reliant on fishing for their livelihood waving from their floating homes.
If looking for somewhere to stay whilst enjoying some local organically grown traditional cuisine, then the green traveler will do well to check out Life Heritage Resort Ha Long Bay, where cruises are offered and all food is prepared using locally sourced ingredients. Delicious.