You build walls out of stone you collect from the field, with a huge amount of effort involved for a long time.

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Thanks to "Scenes From the Stone Age: The Cave Paintings of Lascaux, " at the Field Museum in Chicago, visitors can now see life-size replicas of half a dozen sections of the caves.

WSJ: Prehistoric but Far From Primitive | Cave Paintings of Lascaux | Field Museum | By Mark Yost