The Belgian Ardennes region is a beautiful part of the world, but the question nevertheless arises; what do you with several teenagers if it is pouring down with rain – and I mean sheeting down? One answer is the Grottes de Han, and so that was what we visited today. Nobody was disappointed. I must have been down this massive complex of caves at least five times but each time I return I am fascinated again by the experience. The limestone into which the Lesse river has carved its way is some 360 million years old. The caves themselves are thousands of years old, whilst human beings have probably lived in the entrances to the cave system for a mere two thousand years. For a thousand or so years human beings have been throwing jewelry and lucky charms into the river where it emerges from the rocks after its subterranean journey. (I would have illustrated this post with a picture of a wonderful gold Roman necklace found in the mud at the bottom of the river but my photograph was hopelessly over-exposed.) If you have never been down the Grottes de Han be sure to go. The rock formations and stalagmites and stalactites have there own particular beauty (you can see where the makers of science fiction films such as Alien get their inspiration for wierdly semi-organic backdrops) and the mysterious disappearance of the river into a rock face is fascinating but, above all, the vast sense of time and lengthy geological processes is humbling.