Kong Lor is a river that goes through a mountain. The Hinboun river, swollen by monsoon rains, flows into a vast cave entrance at the foot of a limestone ridge, and travels underground for about seven kilometres before emerging on the other side, in a green valley with rice paddies and buffalo. Visitors go through it in a long, narrow wooden boat, with a boatman at the stern and a guide with a headlamp at the bow, and the experience is a mixture of the ridiculous and the sublime: a tiny light in a gigantic dark space, with stalactites, echoing chambers and the soft slap of the water.
The cave is in the Phou Hin Poun protected area, a region of dramatic limestone karst in Khammouane province, and the village of Kong Lor is the usual gateway. A short walk through the entrance hall leads to the boat landing, and the journey takes a little over an hour each way, with a stop midway where visitors can step out to see formations lit by torches. In the dry season, the water is low and passengers sometimes walk past rapids. The area has become one of Laos's best-loved attractions, and so it can be busy in the middle of the day.
The road to the cave is a highlight of the Thakhek Loop. It winds through karst valleys with rice fields and small villages, with towers of limestone looming over the road. The tarmac is mostly good, but in places it breaks down into potholes or has loose gravel, particularly after rain, and the corners can come quickly. Animals are common on the road. Mornings are the best time for riding, when the air is cooler and the light is soft on the rock, and the mist is rising from the valleys.
There is little in the way of services at Kong Lor beyond guesthouses, simple restaurants and a few shops, so organise fuel and cash in advance, using the larger towns on the loop. Small stalls sell fuel in bottles, but you will not want to depend on them. Evenings are quiet, with the sound of frogs and the glow of lamps, and a river view from a hammock is the ideal way to end the day. Bring a torch of your own, and wear shoes you do not mind getting wet.