Cao Bằng

Angel Eye Mountain - also known as God Eye Mountain or Núi Thủng - is a limestone karst peak in Cao Bằng with a perfectly circular 50m hole piercing through its summit, set in the Thang Hen valley where the surrounding flatland floods into a 15-hectare lake each rainy season.

Bản Giốc is the largest waterfall in Southeast Asia and the fourth largest on a national border in the world - a 300-metre-wide curtain of water crashing across three tiers on the Vietnam-China border in Cao Bằng, surrounded by karst mountains and emerald pools.

Khau Cóc Chà Pass is one of the most dramatic mountain roads in Cao Bằng - a high-altitude route through cloud forest connecting Nguyên Bình to the Phia Oắc massif, with sweeping views over the southern Cao Bằng plateau and valley systems that rival anything on the Ha Giang Loop.

The Mạc Dynasty Citadel in Cao Bằng is one of Vietnam's most overlooked historical sites - a 16th-century mountain stronghold built by the Mạc lords after their retreat from Thăng Long, still partially standing in the borderlands near China.

Nguom Ngao Cave - 'Tiger Cave' in the Tày language - is one of Vietnam's most spectacular limestone grottos: a 2.1km passage of cathedral-scale chambers, extraordinary stalactite and stalagmite formations, and near-total silence, just 3km from Bản Giốc Waterfall.

Pác Bó is where Hồ Chí Minh secretly returned to Vietnam from exile on February 8, 1941, establishing his jungle base in a limestone cave beside the Lenin Stream - the birthplace of the Vietnamese revolutionary movement that would eventually defeat both France and the United States.

Phong Nam Valley is Cao Bằng's most beautiful hidden landscape - a wide flat valley of buckwheat fields, Tày stilt houses, and karst peaks that turns pink and white every October when the buckwheat blooms, earning it comparisons to Ha Giang's Đồng Văn Plateau.

Thang Hen is one of Vietnam's most extraordinary lakes - a cluster of 36 interconnected lakes on a karst plateau at 900 metres elevation in Cao Bằng, their water an intense turquoise-blue from dissolved limestone minerals, surrounded by forested cliffs and almost entirely unknown to international travellers.