Tucked with­in the Phou Hin Boun Nation­al Pro­tect­ed Area in cen­tral Laos are the Kong Lor Caves. This is a riv­er cave sys­tem that stretch­es for more than 7.4 kilo­me­ters, one of the longest in the world. The caves are quite dark, and you might get wet in cer­tain con­di­tions if water is drip­ping from the ceil­ings.