
Laos is a popular tourist destination known for its beautiful scenery and ornate temples, however not many people venture below the surface and discover that what is underground is perhaps even more spectacular.

The wondrous Tham Khoun Ex caves are so exquisite they don't look real at first, which is perhaps why locals believe that spirits inhabit the underground wonderland.

Cave photographer, John Spies, 59, captured the sheer magnificence of the vast, yet intricate, underground wonderland.

Enormous banks of terraced flowstone decorate the walls of the cave in many places. This slowly growing mound of white and orange calcite is one of the larger deposits along the river passage

Rippling reflections: A blue-tinted glow from outside illuminates the entrance chamber of the cave

Not your usual day out! Floating on clear deep water and reflections near the cave entrance, visitors can either bring their own kayaks or rent boats from the local community to paddle deep inside the cave and marvel at its wonders

Tham Khoun Ex caves, commonly known as Xe Bang Fai River caves, feature imposing stalagmitemade of mineral deposits.

With over 15km (nine miles) of awe-inspiring passages and wide expanses of water, it really is one of Laos' hidden treasures.

There is even a vibrant forest thriving at the upstream entrance to the caves, the lush green colour contrasting with the enormous white and orange banks of terraces flowstone that decorates the walls.

Visitors are able to kayak through the waters, or explore adjacent chambers on foot.

The cave is only able to be safely accessed during the dry season from November to April and during this time the water is clear and deep with a rich green hue.

For some of the grander shots, a team of four equipped with powerful LED lights and walkie-talkies helped to light-paint this enormous cavern for this long exposure shot.

In 2008, an expedition, co-led by veteran caver John Pollack lead to the mysterious caves being mapped and photographed for the first time.

What the explorers discovered about the little-known cavern was a vast river cave, which means a cavern with an active water source flowing through it.

'Everything about the cave is big-from its towering entrances to its phobia-inducing spiders, which can be 10inches across,' Pollack told National Geographic.

Nature at its best! The upstream inflow entrance of Tham Khoun Xe has a verdant forest inside a huge collapsed doline. It is possible to kayak from the resurgence to here and back in one full day

Hidden secrets! Massive formations abound in a newly discovered fossil section of the cave, 50 metres above the river level. This section, encrusted with delicate formations and not yet open to tourists, is one of several higher passages that lead to jungle shrouded entrances on

Gigantic! The Giant Gour in the Oxbow area of the cave is 60 metres long and is probably one of the worldís largest rimstone basins

American cave explorer Dave Pierce marvels at giant cave pearls which grow like pearls in an oyster with concentric layers of calcite slowly building up year after year

Lit up! The subterranean passage of the river is spectacularly decorated with calcified formations

Heading into darkness, a visitor paddles a small canoe near the downstream entrance. In the dry season from November to April, the only part of the year safe to visit the cave, the water is clear and deep with a rich green hue

This gigantic section, is also not yet open to tourists, is one of several higher passages that lead to jungle shrouded entrances

The Giant Gour in the Oxbow area of the cave is 196 feet long and is probably one of the world's largest rimstone basins. The pool is filled with water during the wet season. The rims of basins like this grow taller each year as calcite precipitates from cave water as it flows faster over protrusions

The immense proportions of Tham Khuon Xe, one of the worldís greatest river caves, are difficult to photograph. A team of four equipped with powerful LED lights and walkie-talkies managed to light-paint this enormous section for this long exposure shot

Suphaporn Singnakphum stands amongst lush low-light plants in an underground garden in a huge fossil passage that adjoins the inflow entrance of Tham Khuon Xe

Water painting with kayaks and submerged LED lights near the downstream entrance of the cave

Visitors to Tham Khuon Xe can rent canoes or kayaks and paddle upstream to view the stunning calcifications on the cave walls

Sunlight streams into the mist-filled fossil passage near the sink of the Xe Bang Fai River. This section supports a verdant garden of ferns and other low light plants

Water painting with kayaks and submerged LED lights near the downstream entrance of the cave