The Paranormal Intersection: TPI: Linda Moulton Howe: The Alaska Pyramid Mystery

The implications of a massive underground pyramid structure potentially from 10s of thousands, or hundreds of thousands of years ago, would certainly change the perspective of ancient history.

https://www.strangeoutdoors.com/mysterious-stories-blog/alaska-triangle

However, it would be too unsettling for many to consider the possibility of humanity making the climb from the stone age to the space age more than once.

https://www.discovery.com/exploration/Alaska's-Bermuda-Triangle

https://paranormal-intersection.blogspot.com/search?q=Alaska+Triangle

A planet wide catastrophe or a war would cause so much to be destroyed & buried.

https://www.legendsofamerica.com/alaska-triangle

The+Alaska+Pyramid+Mystery if true, could be from an off-world ancient base, or a remnant of a hightech civilization. Either way, there isn't suppose to be any ancient advanced civilization, unless part of history has been lost or suppressed.

https://www.ancient-origins.net/unexplained-phenomena/out-place-artifacts-020544

https://www.ancient-origins.net/unexplained-phenomena/ooparts-found-coal-0010767

https://www.ancient-code.com/five-out-of-place-artifacts-that-challenge-mainstream-history

https://weburbanist.com/2018/09/05/out-of-place-artifacts-the-perpetual-puzzle-of-reverse-engineering-mysterious-objects

https://www.messagetoeagle.com/11-extraordinary-out-of-place-artifacts

https://www.historicmysteries.com/out-of-place-artifact

http://www.ancient-wisdom.com/ooparts.htm

FRINGE was a TV series that hinted of some technology back in very ancient times.

https://en.wikipedia.org/wiki/Mythology_of_Fringe#First_People

https://fringe.fandom.com/wiki/First_People#Assumed_History

A_Canticle_for_Leibowitz was published in 1959. https://en.wikipedia.org/wiki/A_Canticle_for_Leibowitz#Background

If there was a big war in the very distant past, most of the ruins & the tech would have dissolved by now.