Son river, entrance to Phong Nha Cave

The river, whose length is around 30km, flows through Truong Son Mountains to Son Trach commune, Hung Trach district, Quang Binh province, then joins Gianh river and runs into the sea. This is the gateway to enter Phong Nha cave which belongs to Phong Nha - Ke Bang nature reserve complex of Quang Binh province.