Thang Hen Lake

1. Overview of the Thang Hen Lake Complex

Thang Hen Lake is a natural freshwater lake located at an elevation of over 1,000 meters above sea level, within Quoc Toan Commune, Quang Hoa District. The name “Thang Hen” in the Tay language means “the tail of the Pixiu,” as when viewed from above, the lake’s winding shape resembles the tail of this mythical creature. Rather than a single lake, Thang Hen is a complex of 36 natural freshwater lakes nestled within limestone valleys, interconnected by an underground cave system beneath the earth’s surface.

1.1. The Jade-Green Water Phenomenon and Geological Wonders

Thang Hen Lake is renowned for its distinctive jade-green water, which remains crystal clear even during the flood season when nearby rivers often turn muddy with silt. This phenomenon is explained similarly to other waterways within the UNESCO Global Geopark Non Nuoc Cao Bang: the lake water is naturally filtered through ancient limestone (karst) layers and dissolves calcium carbonate (CaCO3) minerals. These particles scatter sunlight at shorter wavelengths, producing a vivid emerald-green hue under the sun.

1.2. The Mysterious “Water-Draining” Phenomenon

One of the most unique features of Thang Hen is its sudden water-draining phenomenon. Every few years during the dry season, the entire lake can be emptied into underground caves within just a few hours, leaving the lakebed exposed with fascinating geological formations. Later, water gradually rises again from subterranean springs, restoring the lake’s original beauty. This phenomenon highlights the complex and mysterious underground hydrological system of the Northeastern limestone region.

2. A Love Legend Intertwined with the Landscape

The poetic beauty of Thang Hen Lake is further enriched by a romantic folk legend of the Tay people, telling the story of Sung and Booc.

2.1. Sung and the Fateful Promise

According to legend, there once lived a handsome and intelligent young man named Sung, who passed the imperial examination and was granted seven days to return home in glory. During this time, he met and married the beautiful Booc. Lost in newlywed bliss, Sung forgot the day he was required to return to the capital. On the final night, he suddenly remembered and hurriedly set off on his journey back.

2.2. The Birth of the 36 Lakes

In the pitch-dark forest, Sung ran 36 steps before stumbling, striking his head against a rock and dying. His 36 footsteps later transformed into 36 lakes of varying sizes within the complex, while the place where he fell became today’s Thang Hen Lake. The tragic yet poignant tale leaves visitors deeply moved as they stand before the lake’s serene waters.

3. Location and Travel Directions

Thang Hen Lake is located about 30km from Cao Bang City in the direction of Trung Khanh, making it an ideal stop before continuing on to Ban Gioc Waterfall.

3.1. Routes and Transportation

From Cao Bang City, travelers follow National Highway 3 toward Quang Hoa. Upon reaching Ma Phuc Pass—one of Cao Bang’s most spectacular mountain passes with dramatic U-shaped curves—signage directs visitors toward Thang Hen Lake. The road from Ma Phuc Pass to the lake is about 4km long, fully paved, and passes through peaceful Tay villages and lush rice valleys.

3.2. Surrounding Ecological Landscape

The lake is surrounded by towering limestone cliffs and pristine old-growth forests. In spring, plum and peach blossoms blanket the area in white, while in autumn, changing foliage paints golden reflections across the water. The scenery creates a true real-life “Forbidden Love Valley,” completely isolated from the hustle and bustle of the outside world.

4. Must-Try Experiences at Thang Hen Lake

At Thang Hen, visitors can fully unwind and immerse themselves in nature.

4.1. Boating and Exploring Subterranean Lakes

The most memorable experience is riding small wooden boats that glide gently across the emerald water to explore narrow gorges and caves around the lake. Visitors can admire stalactites hanging close to the water’s surface and listen to birdsong echoing through the tranquil surroundings.

4.2. Picnicking and Discovering Local Culture

With wide grassy banks surrounding the lake, Thang Hen is an ideal spot for camping and picnics with family and friends. Visitors can also visit traditional Tay stilt houses, sample grilled lake fish, roasted shrimp, and local specialty roast pork from Quang Hoa to fully appreciate the warmth and refinement of highland culture.

5. Practical Tips for Visiting the Mountain Lake

For a complete and enjoyable visit, travelers should keep in mind some practical tips regarding timing and preparation.

5.1. Best Time for Check-in

The period from September to October is considered the most beautiful time to visit the lake. During this season, clear skies and gentle golden sunlight illuminate the water, enhancing its magical jade-green color. This is also the rice harvest season in nearby valleys, creating a vibrant and colorful landscape.

5.2. Packing Essentials and Environmental Awareness

As the lake lies deep within a valley, temperatures can drop in the early morning and at night, so bringing a light jacket is recommended. Above all, to preserve the pristine beauty of this “Forbidden Love Valley,” visitors are encouraged to leave no trash behind, protect the water source, and respect the surrounding ecosystem so that Thang Hen’s jade-green charm remains timeless.