Phys.Org has a story about circular structures found in a cave that have been dated to around 176,500 years ago, before the existence of modern humans. They were constructed from stalagmites that had been broken off,then chopped into similar lengths. The sides of the structures were up to 40 cms (16 inches) in height. There were 2 of them, one 16 square meters (172 sq. feet) and the other 2.3 square meters (25 sq. feet) in area. There is no obvious reason for the construction of the structures. One scientist did say that he could see teenagers doing it. The constructs were fairly deep in the cave, 336 meters (368 yards). Nobody had thought that the Neanderthals would have been caving, so this find is unexpected.
The story is at Scientists: Underground stone rings made by Neanderthals