We also took a day trip outside of Hanoi to see Hoa Lu (the first Vietnamese capital, established by the king who overthrew a millennium of Chinese rule) and Tam Coc (Three Caves). Only ruins remain of the Hoa Lu fortress, but several pagodas are lovingly maintained.
Tam Coc is a waterway that winds between mountains and has carved out a series of grottoes beneath some. It was a beautiful and relaxing journey, although Thông insisted on rowing nearly all the way!