The spectacular boat trip through Phong Nha Cave is an enjoyable though touristy experience beginning in Son Trach town. Boats cruise past buffalo, limestone peaks and church steeples to the cave’s gaping mouth. The engine is then cut and the boats are negotiated silently through cavern after garishly illuminated cavern. On the return leg there's the option to climb (via 330 steps) up to the mountainside Tien Son Cave (60,000d), with the remains of 9th-century Cham altars and inscriptions.
The ticket office and departure jetty are in Son Trach village. Allow two hours to see Phong Nha; add an hour for Tien Son. In November and December, seasonal floods may mean Phong Nha Cave is closed. Weekends are extremely popular with Vietnamese visitors, whose presence is amplified by the spectacular echoes and unventilated cigarette smoke. Note the cave was used as a hospital and ammunition depot during the American War and was heavily bombed.