Ha Long Bay and the Cat Bal Islands are spectacularly scenic. Lot’s cat paw-looking islands dotting the sea, and wooden fishing boats anchored near quite isolated islands. You can take this trip from Hanoi, which is what I’d done. Here’s what UNESCO has to say about Ha Long Bay:
Ha Long Bay, in the Gulf of Tonkin, includes some 1,600 islands and islets, forming a spectacular seascape of limestone pillars. 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.