Steer 300 miles south of Hanoi for today's Geo Quiz. The place in Vietnam we're looking for is a national park.
It's located in north-central Vietnam in Quang Binh Province. The park is mostly jungle. But it offers tourists a lot to explore UNDERGROUND.
There are as many as 300 limestone caves and grottoes -- one of the world's longest underground rivers -- and curious rock formations deep in the ground.
The geological features prompted UNESCO to designate the park a "World Heritage Site" in 2003.
Just last month, a team of British and Vietnamese explorers visited what they say is the largest cave passage anywhere.
"And they says its like a huge underground cathedral."
So what's the name of this Vietnamese national park?
Adam Spillane is just back from an experience that's out of this world.
Well... maybe UNDER this world is more accurate.
Spillane is a member of a British-Vietnamese Caving Expedition that's just returned from exploring a very impressive cave.
Adam...you entered what must be a caver's dream and you have photographs to prove it. What's the name of the cave?
Called Hang Son Doong in Phong Nha-Ke Bang National Park. The answer to our Geo Quiz.