Nhi Thanh grotto houses the Pagoda of Triple Regions (Buddhism, Taoism, Confucianism). Nhi Thanh grotto was closely related to the celebrity Ngo Thi Si when he was the chief of province between 1777 and 1780.

He gave, in a short span of time, a new look to Lang Son in term of politics, economy and national defense. Especially in the domain of culture, he had the merit to discover 8 beautiful landscapes of Lang country including Nhi Thanh grotto. He hired workers to start the renovation of this grotto in 1779. The right side area, being on a relatively more elevated land and the configuration of terrain better, was chosen to be the place for the building of the Pagoda of Triple Regions (in honour of Confucianism, Taoism, Buddhism).

Nhi Thanh grotto lies beneath the Pagoda of Triple Regions. This grotto is a natural cave. The length of a corridor from front entrance to back entrance is over 500 metres with many beautiful and picturesque landscapes. Inscriptions can be seen today on grotto, which were engraved by famous personalities and poets over different epochs. These inscriptions serve as sources of precious historical documents, literary works, information on the history and historical vestiges of Lang Son province. There exists also a very beautiful portray-statue of Ngo Thi Si, engraved in 1779.

Above the grotto is Tam Giao Pagoda, which was built in 1779. The pagoda is dedicated to Confucian, Buddha and Laotze.

Tam Giao Pagoda and Nhi Thanh Grotto is one of the eight sites that attract a large number of visitors in Lang Son.