The Nhi Thanh Grotto is situated in Nhi Thanh Street, approximately 1km from the Lang Son City, Lang Son Province. This Grotto is 600 meters deep. On the cliffs at the entrance are 20 inscriptions that are precious historical and literary documents, including autographs of famous scholars. The statue of scholar Ngo Thi Sy on the cliff engraved in 1779 is a precious work of art. The grotto has numerous stalactites and stalagmites in different shapes.

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.