Tam Thanh Cave

Less than 2 kilometers from the center of Lạng Sơn, a cave opens into a limestone mountain. People have worshipped inside it for centuries, and few would expect to find it in the middle of an urban area.

Lạng Sơn is a mountainous province in the northeast of Vietnam. Tam Thanh Cave does not sit in remote mountain forest. It lies in Tam Thanh ward, in the urban heart of Lạng Sơn, at the top of 30 stone steps cut straight into the side of a limestone mountain. That is exactly what makes the place so unusual. It is a completely natural cave, with huge chambers full of stalactites and limestone vaults, right in the middle of the town.

A flight of 30 stone steps climbs to the entrance, and then the cave opens.

As soon as you pass the mouth of the cave, the temperature changes. The air inside stays cool all year, as limestone caves naturally do. The daylight from outside fades. And ahead lies a space where people have come and gone, prayed and followed a religious life since the time of the Lê dynasty, hundreds of years ago.

The name Tam Thanh comes from Taoism. It points to the three highest realms of that faith, which are also its three supreme gods. The first two are Ngọc Thanh and Thượng Thanh. The third is Thái Thanh. At first, this was a place of Taoist worship. The pagoda's name in Chinese characters is Thanh Thiền Tự, which means "the pagoda of pure meditation". The name speaks of the stillness of a place made for meditation, deep inside the rock.

But this place does not honor only one faith. What sets Tam Thanh Cave apart is that it has been tied to all three teachings: Buddhism, Confucianism and Taoism. Besides Shakyamuni, the founder of Buddhism, and other Buddhas, the pagoda at one time also honored Confucius and Laozi. That shared worship reflects an idea that was very widespread among Vietnamese scholars in past centuries. It is called tam giáo đồng nguyên, the three teachings sharing one root. The three teachings do not shut one another out. They complete one another. Today the layout follows the pattern of the Buddha in front and the deities behind. The front chamber honors the Buddha. The rear chamber honors Thánh Mẫu, the Mother Goddess, together with the gods of folk belief.

High on the rock wall ahead is a carving.

It is a relief of Amitabha Buddha. It stands 202 centimeters tall and 65 centimeters wide. It is not a separate statue set in place: it was cut straight into the limestone wall of the cave. Its artistic style belongs to the Lê and Mạc period, the 16th and 17th centuries. Its two hands point downward, in a gesture called ấn cam lộ. The gesture is a symbol of compassion and of blessings given.

A carver of long ago made this work right on the damp, uneven rock wall of the cave. The carving has survived intact to this day, hundreds of years later.

The stone steles in the cave have their own stories too.

The oldest stele dates from 1677, nearly 350 years ago. It records a restoration of the pagoda inside the cave. It was commissioned by Vi Đức Thắng, a duke who held the title Vũ quận công. He had it made in the reign of Emperor Lê Hy Tông. The stele shows that people cared about this cave, looked after it and restored it again and again across many centuries.

On another wall, lines of Chinese characters are carved straight into the stone. They form a poem by Ngô Thì Sĩ, a celebrated figure of his age.

He was a great scholar of the 18th century. In 1777 he was appointed Đốc trấn of Lạng Sơn, the head official of the province. In his three years in office here, he also left a deep cultural mark. He discovered and named the eight most beautiful sights of the Lạng region, the Bát cảnh xứ Lạng. He ranked Tam Thanh Cave first of the eight. He also built the Tam Giáo Temple, the Temple of the Three Teachings, at Nhị Thanh Cave nearby. He carved poems on the cave wall too. What he did more than 200 years ago still marks this space.

Then there is the stele in Nôm, an old character script for writing Vietnamese. It is the only stele in Nôm in the whole province of Lạng Sơn. It was set up in 1924 by the Tuần phủ, or governor, Đào Trọng Vận. That makes it truly one of a kind.

Deeper inside, two geological features stand out.

The first is a pair of openings called cửa thông thiên, the doors to the sky. They are two natural holes in the vault of the cave that let daylight in. When the light falls straight down at midday, it strikes the stalactites and makes a dreamlike play of light. This is natural optics, not artificial lighting.

The second is an underground lake inside the cave. People call it Hồ Âm Ti, the Lake of the Underworld, and that is a folk name. Its water stays clear and cool all year, and it never runs dry. Stalactites on the ceiling and walls take strange shapes. People from the area and visitors often name them after whatever they seem to resemble. These are folk names given by the people looking, not official scientific names. Anyone is free to find the shapes and name them too.

There is also a bigger picture. In 2024, UNESCO recognized Lạng Sơn as a Global Geopark. Tam Thanh Cave lies inside it. That means the limestone here has value beyond tourism and faith. Its geological value is recognized around the world.

This is a place where nature and faith, geology and history, share one cave in the middle of a town. Walk back down the 30 stone steps and the town returns. Behind you, the light from the two doors to the sky still falls quietly on the stalactites.