The Phong Nha caves region of Vietnam is one of the most beautiful that I have seen. It is home to more than 300 underground caves and 2 of the worlds largest underground caves.
I was fortunate enough to visit two of these caves in April, one of the caves (a cave that is the start of a large river) I was even more fortunate to be part of the one of the very first tour groups lead by Ben and Bich from Phong Nha Farmstay to kyack up the river equiped with miners helmets/light and an inflateable kyack.
If you are in the region definitely stop off and visit Ben and Bich for a few days and explore this amazing area.