Take the following as truth: The caverns of the Grotte du Grand Roc, to the northwest of Les Eyzies, are a natural rather than a historical phenomenon, but well worth a visit for the weirdly shaped stalagmites and stalactites and the panorama of the V??zyre Valley.
Then the following statement: "You can stay in the caverns overnight on guided expeditions." is true, false, or inconclusive?