Deep within the rainforest-covered limestone mountains of Khlong Phanom National Park, just beyond Khao Sok, lies a natural world that has been forming quietly for thousands upon thousands of years.
Kaew Cave, or Tham Kaew (ถ้ำแก้ว), is one of the fascinating caves found among the dramatic limestone mountains of Surat Thani. Hidden behind dense tropical vegetation, the cave contains chambers filled with stalactites, stalagmites, mineral deposits and unusual rock formations created by one of nature’s slowest processes.
But how did Kaew Cave get here? And why does it sparkle when you shine a light across its walls?
To understand that, we have to travel much further back in time than the rainforest growing above it today.
The Limestone Mountains of Khlong Phanom
Khlong Phanom National Park covers approximately 410 square kilometres of Surat Thani Province and is characterised by steep, complex limestone mountains covered in tropical evergreen rainforest. The area is also an important watershed feeding the Tapi River system.
These limestone landscapes are part of the wider karst scenery for which southern Thailand is famous.
Look across Khao Sok, Khlong Phanom and neighbouring parts of Phang Nga and Krabi and you’ll see the same extraordinary landscape: enormous limestone cliffs rising almost vertically from thick tropical forest.
The story of caves such as Kaew Cave begins with this limestone.
A Landscape Born Beneath Ancient Seas
Long before Thailand looked anything like it does today, parts of what is now southern Thailand were covered by ancient tropical seas.
Over immense periods of geological time, the remains of marine organisms containing calcium carbonate accumulated on the seabed. Layer after layer eventually became compressed and cemented into limestone.
Later geological forces uplifted and fractured these limestone deposits, eventually creating the mountains that dominate the landscape around Khlong Phanom today.
But creating the mountains was only the beginning.
Water would create the caves.
How Kaew Cave Was Formed
Kaew Cave is officially classified as a solution cave, meaning that it developed as water gradually dissolved the limestone. A geological cave survey records Kaew Cave as having a surveyed total length of approximately 368 metres.
The process sounds simple, but it takes place over enormous periods of time.
Rain falling onto the rainforest absorbs carbon dioxide from the atmosphere and, particularly, from the organic-rich soil.
This creates a very weak carbonic acid.
The water then works its way through tiny cracks and fractures in the limestone.
Drop by drop, year after year, the slightly acidic water reacts with the calcium carbonate within the rock and slowly dissolves it.
Tiny cracks become wider.
Wider cracks become passages.
Passages eventually become chambers.
Over geological timescales, water can transform apparently solid mountains into enormous underground networks.
Kaew Cave is part of the result.
The Cave Didn’t Stop Changing
Once passages and chambers had developed, another geological process began creating the extraordinary formations visitors see today.
Water continued travelling through the limestone above the cave, carrying dissolved calcium carbonate with it.
When droplets reached the cave ceiling, changes in pressure and carbon dioxide caused tiny amounts of calcium carbonate to be deposited.
One drop leaves almost nothing.
Millions of drops are a different story.
Slowly, mineral deposits begin growing downwards from the ceiling. These are stalactites.
Where water falls onto the cave floor, minerals can accumulate upwards to create stalagmites.
Given enough time, the two can eventually meet and form a limestone column stretching from floor to ceiling.
Water flowing across walls and sloping surfaces can also produce sheets, curtains and rippling formations.
It is effectively natural sculpture performed by water, minerals and time.
Why Is It Called “Kaew Cave”?
This is where the cave becomes particularly interesting.
“Kaew” (แก้ว) can refer to glass or crystal, and the name becomes understandable once you venture inside.
Certain mineral-covered surfaces within the cave reflect torchlight, creating a shimmering, almost crystalline appearance.
Official tourism information describes sections of the cave walls as containing curtain-like formations and sparkling mineral crystals that appear similar to tiny pieces of glass.
That glittering effect ultimately gave Tham Kaew – Kaew Cave – its name.
Humidity can make the experience even more dramatic. During the rainy season, increased moisture inside the cave can intensify the appearance of different minerals and colours within the rock.
Turn off your torch, however, and the transformation is immediate.
Complete darkness.
The mountain becomes silent again.
The Chambers of Kaew Cave
Kaew Cave isn’t simply one enormous empty cavern.
The accessible cave is divided into a series of chambers, many of which have been named after the unusual formations found inside.
Four particularly recognised sections are Kled Kaew Chamber, Ruesi Chamber, Seahorse Chamber and Medicine Pot Chamber.
Kled Kaew – The Crystal Chamber
Perhaps the formation most closely associated with the cave’s name, this area contains mineral surfaces that sparkle when illuminated by a torch.
Move the beam of light and tiny reflections appear across the rock.
Ruesi Chamber
Here, one of the formations resembles a traditional hermit or ruesi figure.
Like looking at shapes in clouds, many cave formations have acquired names because generations of visitors recognised familiar objects, animals or figures within the stone.
Seahorse Chamber
One of the cave’s most unusual areas contains numerous hanging formations whose shapes have been compared to tiny seahorses.
Official descriptions mention large numbers of these unusual formations appearing together.
Medicine Pot Chamber
Another formation resembles a traditional medicine pot, giving this chamber its name.
Together, these rooms turn a journey through Kaew Cave into something resembling a walk through a completely natural underground gallery.
Except every sculpture has been created by water.
A Cave Hidden Beneath the Rainforest
Part of what makes Kaew Cave special isn’t simply what lies inside.
It’s where it is.
The cave sits within Khlong Phanom National Park, surrounded by steep limestone mountains and some of southern Thailand’s lush tropical rainforest.
Reaching the cave itself requires some effort.
Kaew Cave lies approximately two kilometres from the national park headquarters, with the final approach involving a roughly 919-metre walk alongside steep mountain terrain, taking around 30 minutes under typical conditions.
That journey creates a wonderful contrast.
One moment you’re surrounded by humid rainforest, insects, birds and enormous tropical plants.
Then you step into the mountain.
The temperature changes.
The light disappears.
The sounds of the jungle fade.
And suddenly you’re standing inside a landscape that has been developing on a geological timescale.
A Landscape That Is Still Being Created
Perhaps the most fascinating thing about Kaew Cave is that its story isn’t finished.
Whenever rain falls onto the limestone mountains above Khlong Phanom, water begins another journey through the rock.
Some will flow into streams.
Some will feed the surrounding rainforest.
And some will disappear underground.
That water will travel through cracks in the limestone, carrying dissolved minerals before eventually emerging as tiny droplets somewhere inside the cave.
Drop.
Pause.
Drop.
Each one potentially leaves behind an almost microscopic layer of mineral.
It isn’t something we can watch happening.
The timescale is simply too slow.
But over centuries and millennia, those tiny deposits become stalactites, stalagmites, curtains, columns and strange formations that future generations may one day give entirely new names.
Kaew Cave: A Journey Through Deep Time
Visiting Kaew Cave isn’t simply about walking into another cave.
It is an opportunity to see the geological story of southern Thailand from the inside.
The limestone mountains towering above Khlong Phanom are impressive enough from the rainforest floor. But step beneath them and you discover another landscape altogether – one shaped by ancient seas, geological uplift, tropical rainfall and the almost unimaginable patience of water.
Every chamber represents thousands of years of change.
Every stalactite began with a drop of water.
And every sparkling mineral surface is part of a geological process that continues today.
The rainforest outside might feel ancient.
But the mountain beneath it has a story that goes back much, much further.
