Phong Nha is located in the centre of the middle part of Vietnam , South West of the Giang River, about 40kms NorthWest of Dong Hoi city. The Western boundary of the park is part of the Laos-Vietnamese border. The park borders another limestone zone of Hin Namno in Laotian territory. This area has been nominated as a World Natural Heritage Site.
I've cycled here 5 times and visited the caves twice because of the caves' beauty and the military historical value of the place. Situated on the Ho Chi Minh trail the caves played a major role to the North as it was situated right smack on this important supply route to the South during the Vietnam war.
It's possible to canoe about 10 kilometres into the cave, but it's known to go much deeper going in by foot . It was used extensively by the North Vietnamese army to shelter their soldiers and supplies during the war against South Vietnam and the Americans. I am told the cave was a military hospital for wounded soldiers and after being through myself I can concur that it would have been a perfect location for a secret hospital, supply and weapons cache , and stop over point for the North Vietnamese Army hoofing by foot to fight in the South which in itself was a 3 to 4 month journey along the Ho Chi Minh trail, I could envisage it as being quite a secret and secure location as mentioned above, but once the Americans discovered it as a strategic location they launched many aerial bombing missions against the caves to no avail other than to destroy ancient stalactites close to the entrance and partial bombing damage to the entrance of the cave., quite a relief to the occupants on the inside I'm sure.
National geographic gives a detailed history on the caves from when they were first discovered in the 1940s up until now. Defiantly worth a visit.
Some photos here from my last visit with a group of Vietnamese war veterans who were based at the Phong Nha caves and/or were hospitalised there during the Vietnam war