It is accessible by road and rail from Hanoi, the Vietnamese capital, and it is the northernmost point on National Route 1.

Due to its geography as Vietnam's gateway to China (being located just across from Guangxi), Lạng Sơn (諒山) and its ancient citadel have been in the path of many invasions, and were the site of three French defeats during the colonial era.

It was evacuated in 1950 during Võ Nguyên Giáp's offensive against the French border forts, considered a turning point in the Indochina War.

[3] The surface rocks in the area are a Permian limestone, overlain by the early Triassic Lang Son Formation, consisting of flyschoid beds with interbedded sandstones, siltstones and clay shales and some felsic volcanics.

The half hilly region surrounds a plain with an average elevation of 10 m from north-east - north to north-west – south-west and south – south-east.