Over (pictured), one of the caves inside the Phong Nha - Ke Bang National Park.
During the rainy season, which runs from September to February, these cascading pools fill with water.
As water percolates through the limestone strata, it dissolves and carries minerals, particularly calcium carbonate.
When this water flows into the cave, chemical changes cause the minerals to precipitate, forming natural stone rims that gradually create the pools.
The cave was discovered in 1997 by an expedition team from the British Cave Research Association.
It measures 3.2 kilometers in length, with an entrance roughly 30 meters wide and 25 meters high.
Inside, the cave has a maximum height of 103 meters and width of 125 meters.
During the rainy season, visitors can explore the unique beauty of these natural pools amidst the magnificent cave setting, provided weather and safety conditions permit.
As the volume of water seeping through increases, the pools gradually fill up, reflecting the surrounding rock formations and stalactites.
Over cave also has an array of stalactites and stalagmites in all kinds of shapes and sizes.
The cave is part of a tour for visitors that also takes them to Dai A and Pygmy caves.
There are several itinerary options: a 2-day, 1-night tour priced at around VND8 million (US$308) per guest, a 3-day, 2-night option for VND12 million, and a 4-day, 3-night one for VND35 million.
Thang cave discovered in June in the core zone of the national park too has massive emerald-green pools.
It also has a grand system of speleothems, including stone columns up to 50 meters tall and cave pearl clusters, earning it reputation as a stalactite "palace."
Stalactites hang from above, hovering over crystal-clear calcite pools below. During the dry season, most of these pools dry up.
The cave was opened to tourism in August, with a 2-day, 1-night tour priced at VND7.6 million (US$294) per guest.
When water levels drop, the pools dry up and expose stone steps, revealing the tiered geological structure of the cave floor.
In Thung cave, there are two distinct types of calcite pools.
Standalone ones are typically large.
Because water flowing strongly through the ceiling or walls erode the cave floor to greater depths, forming large reservoirs.
On average, they are 30 to 60 square meters in size.
A rimstone pool inside Thung cave.
Thung also has numerous underground rivers and a massive sinkhole near its center created by geological processes.
Opened for tourism in 2023, the cave is accessible through a 3-day, 2-night Hung Thoong exploration tour priced at VND12 million.
Phong Nha - Ke Bang National Park was recognized as a UNESCO world natural heritage site in 2003 and 2015, has a core area of 123,326 hectares and a buffer zone of 220,055 hectares.
It has nearly 500 caves, with around 40 currently open to tourism, including Son Doong, En, and Pygmy, the world's largest, second largest, and fourth largest caves.
