A cosmic impact about 12,800 years ago caused the Younger Dryas – a glacial surge which reburied the world in ice for a thousand years. So not an Ice Age, but a chill-down. The same events probably caused the extinction of a multitude of species and obliterated any human culture unable to adapt to the cold.
A candidate crater has been spotted deep under Greenland’s ice sheets… Greenland ice sheet hides huge ‘impact crater’
At the time, or close to, humans built this mystery structure…
No one knows what it was for, but a good guess is that it was an astronomical structure, designed to map the sky at the time. If small impactors are raining down from the sky regularly, it has a clear purpose.