The Nam Hin Bun river does something rivers rarely do: it walks straight into a mountain and comes out the other side. At Kong Lor, in the Khammouane province of central Laos, it flows into a limestone tunnel about seven kilometres long, passing beneath the great karst ridge of the Phu Hin Bun, and visitors can travel through it in long narrow boats with outboard motors, in near-total darkness, with only a headlamp to light the way. The cave roof rises as high as ninety metres in places, and the formations, in places lit by coloured lamps, are impressive.
The trip takes an hour or two in all, and at the far end, the boat emerges into a green valley, with a rest stop where you can wait for the return. In the dry season, from November to April, the water is shallow in places, and passengers may have to get out and wade while the boatman drags the boat over rocks. In the rainy season the river is fuller but also stronger. Tickets are bought in the village of Ban Kong Lor, and a guide goes with each boat. The cave is spectacular, and the silence between engine noises is deep.
The Thakhek Loop, of which this is the finish, is one of the great motorcycle journeys of Southeast Asia, a circuit of around four hundred kilometres through limestone mountains, rice valleys, rivers and villages. The roads vary from smooth asphalt to broken surface and gravel, and the scenery is wild and beautiful, with green cliffs rising out of the paddies. Traffic is light, the people are friendly, and the pace is relaxed. Water buffalo, dogs and chickens share the road, so slow down.
Practical matters need some planning. The nearest town of any size is Ban Nahin, on the main road, where you can find fuel, food and basic repairs, and it is wise to fill the tank there. In small villages along the loop, petrol is sold from bottles at roadside stalls, and while it works in an emergency, quality varies. Carry water, cash in Lao kip, and a rain jacket. Mobile signal is patchy in the valleys. Guesthouses at Ban Kong Lor offer simple rooms and meals of sticky rice, grilled fish and spicy dips, and the sound of the river at night is a pleasant lullaby. Rain in the wet season, from May to October, can make the roads muddy.