You can come to Dong Hoi in Vietnam to visit Phong Nha National Park by airplane, train, bus, motobike or taxi.
Currently, the closest service is via Vietnam Airlines to Dong Hoi, check their website for latest fares and flight times.
Several arrivals and departures at Dong Hoi daily from as far away as Hanoi and Ho Chi Minh City, only a few hours from Hue.
A local bus goes from Dong Hoi to Phong Nha for 40,000 VND. It departs at 14:00 from Nam Ly bus station. The bus back to Dong Hoi leaves Phong Nha at 8:00, so you have to either stay overnight or try to go back with one of the tour buses (they may even take you to Dong Hoi for free).
Motorbikes can be rented for 150,000 VND from hotels in Dong Hoi. It takes about 1 hour via a highway that has little traffic: the Phong Nha cave is about 45 km from Dong Hoi and the Thien Duong (Paradise) Cave is about 70 km from Don Hoi.
Taxis can be hired from hotels/resorts, airport or train station in Dong Hoi. About 1 hour on a highway with cars, oxcarts, motorbikes, buses, trucks.
Tours are available from Hue.Hotels in Dong Hoi can arrange day trips to the park.