Hidden beneath the limestone cliffs of Thung Nham in Ninh Binh, the Mermaid Cave - or Dong Tien Ca - is capturing the imagination of both Vietnamese and international travelers. Its winding, water-carved passageways stretch for more than 500 meters, creating a cool, enclosed space of natural mystery and allure.

To reach the cave’s entrance, visitors must first cross a narrow iron bridge and climb a series of stone steps. From there, they descend roughly 40 metal stairs deep into the mountain, where an entirely new world awaits - one that feels far removed from the surface above.

Unlike most water caves that require a boat, the Mermaid Cave invites visitors to explore on foot. A floating walkway winds through the limestone interior, guiding travelers across shimmering pools and beneath intricate formations of stalactites and stalagmites. Many consider it one of Thung Nham’s most beautiful caves for its ethereal, dreamlike scenery.

The cave’s name stems from its landscape and cool underground stream, which evoke the feeling of being beneath the sea. Over millions of years, nature sculpted countless rock shapes that resemble coral reefs, cascading diamond-like waterfalls, dolphins, elephants, and crocodiles - each glittering faintly under the play of light filtering through crevices in the stone.

In the middle of the cave, an opening reveals a glimpse of the surrounding forest and cliffs. According to the Thung Nham tourism site’s representatives, the cave was once called “Hang Ca” (Fish Cave) because it was home to two rare fish species - the royal snakehead and the Tong Truong perch. These cold-water fish, native to the limestone springs of Truong Yen and Thung Nham, were once considered delicacies worthy of being offered to kings.

The cave water remains crystal clear, cool enough to see to the bottom. Long ago, formations said to resemble a sleeping mermaid appeared inside, though erosion has since blurred their outlines. Today, a finely sculpted mermaid statue carved from stalactite rock stands in their place, offering visitors a beautiful photo spot.

Many travelers liken the Mermaid Cave to a precious gem bestowed by nature - serene, sparkling, and alive with color. Its green-tinted water reflects the rocky ceiling above, while sunlight seeping through cracks creates shifting contrasts of light and shadow, enhancing its mystical charm.

For visitors, walking through the cave is an intimate experience. Some passages are so low that one must bend or crawl to pass; others curve like a mermaid’s tail, leading eventually to a small exit bridge that opens back to the forest and fresh air.

The Mermaid Cave stands as a symbol of Thung Nham’s unique appeal - an invitation to step quietly into the heart of the earth, where time, water, and stone have conspired to create a world both ancient and wondrous.