Kong Lor is a river cave seven kilometres long in central Laos, and you get through it by boat, in the dark. A narrow longtail takes three passengers and a boatman, the motor droning between the walls, a pole taking over where the water runs shallow. Your headlamp finds a wall, then the water, then nothing at all for minutes together. What it never finds is the roof. What tells you how big the chamber overhead is turns out to be sound: the engine note opens out and comes back late. If the boatman cuts the motor and poles for a stretch, the dark closes in completely. Some way in, everyone steps ashore and walks a lit path through stalagmites, columns and stone draperies, the only part of the cave you see properly. Meanwhile the boatman hauls the empty boat up the rapid you have just walked around.
One pool glows a bright emerald that villagers hold to be the skin of the god Indra, and the same green shows outside where the river leaves the rock. After nearly an hour of black water the passage brightens and the longtail slides into daylight at the Natane mouth, the river spilling into a pool clear enough to count the stones on its bottom. From there you look back at the cliff and watch the whole Nam Hin Bun pour out of the mountain you just crossed. The valley on this side is reachable only through the cave or over five mountain passes, and its rainfed paddies turn gold in October. This is not a curiosity but a road, and the boatmen grew up on this river. The villagers below the mountain are said to have found the tunnel in the sixteenth century, after an unfamiliar duck turned up on the pool at its mouth. Bundles of rice seed and a carved buffalo yoke drifted out of the rock next — proof that somebody was living on the other side. A party went in by torchlight, spent three days in the dark, came out into an empty valley and founded villages in it.