Amazing what gets done when there's no cable TV

So where were you 500 years before the Egyptian pyramids were constructed?  Or Stonehenge? That's when the folks north of Dublin completed the Bun Na Boinne (New Grange) and Knowth cairns using stone age tools. The large domes were well engineered utilizing large flat sandstone floated and carried from 30 km away anchored the walls. Interior chambers were built for some sort of ceremonial purposes, then the whole thing was covered in many meters of soil.

The really "wow" part is that the main doorway, which was unearthed about 1960, is situated such that the deepest recesses of the interior chamber is illuminated by the sunrise on the winter solstice. As an agricultural society they would have paid close attention to the weather for centuries and has some way of charting the shortest days, knowing warmer times were on the way.
Amazing on several points: that thousands of folks were well-fed enough to exert the effort, that they ultimately abandoned the area after a while despite all the effort, and what's possible if not distracted by TV or phartsmones.
Or maybe it was just aliens.