Đồng Hới
It is the closest city to Phong Nha-Kẻ Bàng National Park , UNESCO's World Natural Heritage Site , 50 km north . 
<triplet> Phong Nha-Kẻ Bàng National Park <subj> World Natural Heritage Site <obj> heritage designation <triplet> World Natural Heritage Site <subj> UNESCO <obj> maintained by