Dunwich Borers is a myth location in Fallout 4.
It is believed by many players that apparitions can be seen in the quarry of people who worked there before the war. Many believe this to be a strong possibility because of the haunted Dunwich Building in Fallout 3.
Before the war, the site was owned by Dunwich Borers LLC, a company that manufactured rock drills for tunnelling and drilling.
When exploring the interior of the quarry, the player will experience flash backs. These flash backs show many apparitions from the past before the Great War. Other than these flash backs, there is a constant eerie feeling like someone is always behind the player, hiding in the shadows, a type of paranoia. It is believed that these 'spirits' are trying to warn the player about the evil presence and satanic rituals located deeper within.
Overall, the hallucinated flash backs appear to be caused by one of two things; paranoia, or a hallucinogenic drug substance in the air.