Deep in a dark cave in southwestern France lie half a dozen mysterious structures that scientists believe were built by Neanderthals 176,000 years ago -- about 140,000 years before the first modern humans arrived in Europe. The structures, described Wednesday in the journal Nature, are located in what is known as the Bruniquel Cave. They are made of roughly 400 pieces of stalagmites, all roughly, almost eerily, the same size. Archaeologists say these mineral formations were probably broken off the cave floor by ancient hands and then deliberately arranged into two large rings and a series of four round piles...