Tham Phay Cave

Beyond the famous Ba Bể Lake, the old Ba Bể area holds places that far fewer people know. Thẳm Phầy Cave is one of them.

A document from the Bắc Kạn provincial department of culture, sports and tourism lists Thẳm Phầy as one of the area's beautiful natural caves. It lies in Nà Slải hamlet, in Hoàng Trĩ commune. Bắc Kạn merged with Thái Nguyên province in July 2025. The former Hoàng Trĩ area now belongs to that province. A Thái Nguyên newspaper also mentions the cave in connection with the new Đồng Phúc commune.

The cave goes by several names. The spelling varies, and news reports say people in the area also call it "hang Lửa", the Fire Cave. That is a popular name, not an official one.

What sets Thẳm Phầy apart is the kind of cave it is. It is not a dry cave with a flat path and brightly colored lights, like many caves opened to tourists. It is a water cave. In 2016, a Tuổi Trẻ newspaper reporter went inside and recorded what was there: an underground stream, dripstone formations of many shapes, and veins in the rock worn lengthwise by water. In places the water reaches only the knee, and in places it runs deeper than the waist. After more than a kilometer, the cave splits in two. One branch cuts deep into the mountainside. The other goes into the heart of the mountain, where the water is quite deep.

A Thái Nguyên newspaper describes the trekking tour to Thẳm Phầy as an experience of nature, caves and local culture. It says the tour helps put Ba Bể on the map of adventure travel.

Some have heard the cave called the Sơn Đoòng of Ba Bể. Sơn Đoòng is a cave in central Vietnam, known as one of the largest in the world. That is the press's way of suggesting the cave's scale and wildness. It is not a scientific conclusion or an official ranking. Thẳm Phầy is a beautiful cave, still wild in the true sense of the word, and it needs no comparison.

It is an adventure water cave, and it has no official tourist route. Tuổi Trẻ reports that a survey team turned back when the water underfoot ran faster and word came that rain was on the way. That was the right decision. Rain falling upstream can make the water in the cave rise and run fast within minutes, even when no rain is falling outside.

Thẳm Phầy is one of the most intact natural corners of the Ba Bể area. A guide stands still and raises a lamp. The light falls on tier after tier of ivory-white dripstone, and the dark, shining water gives it back like a mirror. The sound of the underground stream echoes from the right-hand branch, where the cave runs into the mountain and no one has measured it to the end.