Phra That Nong Khai (aka Phra That Klang Nam) is the remains of a 400 to 600 year old temple that collapsed into the Mekong River in 1847.
Subsequent erosion left the stupa now in the center of the river. It is only visible during the dry season and low water levels of the Mekong River.
Nong Khai people decorate the small part above the surface with flags.
A newly constructed replica of the original temple was built in 2006 on the riverbank close to its original location.
Just follow the promanade along the Mekong River towards the Thai-Lao Friendship bridge.