The Ha Long bay, dotted with 3000 limestone islets rising from emerald waters, is the best known natural wonder of Vietnam. Because of their precipitous nature, most of the islands are uninhabited and unaffected by a human presence. The site's outstanding scenic beauty is complemented by its great biological interest. The islands feature endless numbers of beaches, grottoes, and caves. Ha Long means "where the dragon goes into the sea". According to a legend, as a great dragon who lived in the mountains ran towards the sea, its tail gouged out valleys which later filled out with water, leaving only bits of land over the surface, the many tiny islets. Because the distances are actually quite large, it is preferable to hire a fast boat for the tour. Of the two gateway towns, Bai Chay's development is due mostly to tourism's, while Hon Gai has kept its where mining activity and fishing boats.