Quảng Bình is a province in central Vietnam, bordering Laos to the west and the South China Sea to the east. The capital Đồng Hới is known for the remains of its star-shaped 19th-century citadel and the long sandy stretch of Nhật Lệ beach. The city is a base for accessing the Phong Nha-Kẻ Bàng National Park, featuring mountainous jungle and many limestone caves including the massive Sơn Đoòng Cave.