I'm not quite sure the date we visited here but we took a trip to a Jomon Era archeological site. There are 17 sites and some were added to the World Cultural Heritage list in 2021. I dated this post from 2009 so I can keep it in chronological order.
This site was occupied from 3900 to 2200 B.C. It started out as a storage place for nomadic peoples but ended up as a big village. The remains of about 500 pit houses were found in this area.
The site was discovered in 1992 when a baseball stadium was under construction. The stadium was moved somewhere else and the area was preserved.
This large wooden structure might have been a monument, a watch tower, a shrine or a lighthouse. No one knows exactly why they were constructed. Only the bottoms of the large pillars of the structure were found but engineers figured out the dimensions from that. And there were other six-pillared structures like this one in the area so they that information to help them. All the towers all faced in the same direction so there is probably some significance to the way they face.