The underground tunnels and buildings.
Did they the Enemy build them ALL?
Or
Did most already exist?
Previous cities buried.

Have been following a chap with a YT channel called Archaix. He is a chronologist and has extensive study in this subject. He has discovered multitudes of evidence that we have a reset of sorts EVERY SINGLE 138 years - regardless of what calendar we 'use'. Every 3 or 4 138 years is a big one. They thought the last one in 1902 was the biggy so they went underground for a while. When they realised it was only a localised event, they resurfaced and all these inventions suddenly appeared, and most of the Fortune 500 companies were created. They covered up history around that time so we wouldn't have the evidence, but a few bits survived. Fascinating stuff, next one due in 2040. There are also other events that happen that are independent of the 138 years one, but he calls it the Phoenix Phenomenon. Coincidentally, the USA great seal used to be a Phoenix. And the Masonic book (can't remember the name), for the Level 33 it just has a picture of a Phoenix, and no content.