Phong Nha–Ke Bang, often referred to as the “kingdom of caves”, is home to more than 425 discovered ones, around 50 of which have been opened to tourists.Phong Nha – Ke Bang: untapped biological treasure in Truong Son mountainsPhong Nha – Ke Bang becomes Vietnam’s first transboundary Natural World Heritage siteBeneath Vietnam’s forest, a cave system ranks among Southeast Asia’s longest