The Marble Mountains.

Rising abruptly from the coastal plains just south of Da Nang, the Marble Mountains are a cluster of five limestone and marble hills named after the natural elements. The primary draw is Thuy Son (Water Mountain), where a network of stone staircases connects centuries-old Buddhist pagodas, hidden shrines, and cavernous grottoes carved directly into the rock. Inside Huyen Khong Cave, shafts of sunlight pierce through a collapsed ceiling to illuminate giant stone Buddhas, while the dramatic Am Phu Cave offers a stark descent into a Buddhist depiction of purgatory. Climbing past the shrines leads to breezy summits with panoramic views of the East Vietnam Sea and the changing city skyline. It is a atmospheric mix of active pilgrimage site, wartime hideout, and natural labyrinth.