Thang Hen Lake – The Emerald “Fairyland” Among Cao Bang’s 36 Mountain Lakes
Cross Ma Phuc Pass and turn onto a narrow road winding through rugged limestone peaks, and you’ll be surprised by an emerald lake tucked into a valley. Mountain cliffs and ancient forest surround it, reflected in the water. This is Thang Hen Lake, the largest of Cao Bang’s 36 mountain freshwater lakes, known among young travelers as a “fairyland.” Beyond its beautiful scenery and legends, Thang Hen is a full-service eco-tourism destination, with lakeside and cave visits, outdoor activities, dining, and overnight stays.
Where Is Thang Hen Lake?
Thang Hen Lake is in the former Quoc Toan Commune. In July 2025, Quoc Toan Commune, Tra Linh Town, and Cao Chuong Commune merged to form the new Tra Linh Commune.
Featured image of Thang Hen Lake in Tra Linh Commune
The lake is about 30 km northeast of Cao Bang city center. Suggested route: take National Highway 3 for about 21 km from the city, turn onto Provincial Road 205 for about 4 km, then follow signs to Thang Hen Lake Eco-Tourism Area for another 8 km. The stretch over Ma Phuc Pass is especially scenic, so take your time and stop to enjoy the views.
Why Is It Called “Thang Hen”?
The lake is diamond-shaped and deep green year-round, hidden behind ancient forest and rugged limestone peaks. The Tay people thought it resembled the tail of a bee, so they named it Thang Hen, meaning “bee’s tail” in the Tay language.
In 2001, the Ministry of Culture recognized Thang Hen Lake as a national scenic site.
A Network of 36 Lakes Beneath the Mountains
Thang Hen is the largest of 36 freshwater lakes in the Tra Linh area. They may look separate, but underground caves connect them. Other lakes near Thang Hen include Thang Vat, Na Ma, Thang Loong, and Thang Hoi.
Researchers say Thang Hen is part of a chain of lakes running along a limestone valley. They formed when rock above an underground channel of the Tra Linh River collapsed. The entire lake system lies in a broad valley between the former Quoc Toan and Ngu Lao communes. The lakes are spaced a few dozen to a few hundred meters apart.
A Lake That Never Turns Murky
The water stays emerald green all year, even during floods, when other lakes in the area turn muddy red. The secret lies in Thang Hen Cave, high above the lake, where clear water flows down to fill it. On the northeastern side, the cave opening juts over the water like the head of a dragon that has slept for thousands of years. It’s the best spot for photos of the lake.
The Legend of Sung and His 36 Steps
The Tay people tell of a handsome, clever young man named Sung who lived in Cao Bang long ago. After passing the imperial examinations and becoming an official, he was granted seven days by the king to return home in triumph and pay his respects to his ancestors. Back in his village, he married the beautiful Booc. So devoted to his new wife was he that he forgot when he had to return to the capital. He remembered only on the seventh night, then hurriedly said goodbye and ran through the darkness.
After 36 steps, he fell, struck his head on a mountain, and died. His 36 steps became the large and small lakes around Thang Hen. The rocky caves around the lakes mark where his toes caught on the ground, while the place where he fell is today’s Thang Hen Lake.
Three Attractions in One Complex
Within the resort grounds, just a few minutes’ walk from the lake, are two limestone caves. One ticket gives you access to all three attractions.
Ham Huong Cave can hold more than 100 people. Step inside to feel the cool air and see stalactites formed over thousands of years.
Thanh Binh Cave is just a few hundred meters from Ham Huong and is larger. Its spacious interior makes it a great place to rest after walking around the lake.
Editor’s tip: Visit the lake first, then Ham Huong Cave, followed by Thanh Binh Cave. Enjoy the lake while the light is good, then escape the midday sun inside the caves.
Activities, Dining, and Overnight Stays in One Place
Thang Hen Lake Eco-Tourism Area covers more than 30 hectares and has everything you need for a full day out or an overnight stay.
Picnics and outdoor activities. Admission includes access to the picnic area, a traditional communal house, and rest huts. It’s an ideal spot for families, groups of friends, and organized outings with activities by the lake.
Trekking and nature watching. Walk around the lake to see nearby smaller lakes, or trek to Thang Mong Prairie, where natural green grass carpets the landscape. Doves, partridges, and golden monkeys live around the lake, so if you arrive early and keep quiet, you may spot them.
Dining. The resort has dining services for visitors. The camping package also includes an outdoor BBQ dinner and breakfast served at your tent.
Stay overnight by the lake. You have two options:
- Glamping: Stay in a luxury tent with picnic accessories, welcome drinks, music under the moonlight and breakfast served at your tent. Wake up to views of the lake right from your bed.
- Stilt house: Stay in a traditional local stilt house and experience community life in the highlands.
Spending a night by Thang Hen Lake, listening to the mountain breeze and watching mist lift from the water at dawn, is an unforgettable experience you can’t get on a day trip.
When to Visit
Summer brings plenty of rain, and the lake is at its fullest and bluest. In winter, water levels drop, so there are fewer visitors. September and October are the best months to see the lake recede, and the mild weather is ideal for mountain drives and camping.
Nearby Attractions
Angel Eye Mountain lies within the Thang Hen Lake cluster in the Non Nuoc Cao Bang Geopark, making it easy to visit both on the same trip.
Visitor Tips
- Stay safe by the lake: The lake is deep and has underground caves. Do not swim, especially when the water level is falling.
- In the caves: Wear shoes with good grip, as the ground can be slippery. Do not touch or break the stalactites, litter, or bring food into the caves, in accordance with site rules.
- When camping: Light fires and barbecue only in designated areas, and clear away all rubbish before you leave.
- Mountain roads: Check your vehicle carefully and avoid driving in heavy rain.
- What to bring: A jacket for chilly nights in the highlands, and insect repellent if you’re staying overnight.
- How long to spend: Allow half a day to visit the lake and two caves. Stay overnight for the full experience.
Thang Hen Lake is beautiful for more than its jade-green waters and reflected mountain cliffs. It is also home to a rich collection of Tay folk tales, stalactite caves, green grasslands and moonlit camping nights. When you visit Thang Hen, stay a little longer. You’ll understand why this “fairyland” leaves visitors reluctant to go.
