Of the several cave complexes in the Ardennes, this one is probably the most spectacular and worth visiting. Only about one-fifth of the cave is open to the general public, though other parts are accessible to experienced speleologists. Guides take visitors on an hour-long tour to see the stalagmites and stalactites, marvel at the sometimes bizarre and sometimes graceful shapes taken on by the limestone rock of the caves, and listen to the echo in the great subterranean chambers carved out by the Lesse River. The highlight is a brief boat trip on an underground river.