About 75 years ago, on one Halloween it was swallowed up by an earthquake, taking the whole family with it. Darrow University was built over the old mansion site.
The old Mystery Incorporated investigated the buried building, unaware they were being observed by the mad surviving Darrow, Danny. He listened to them enough to get all their names and an idea of their personalities. He filled the place with traps for them, but they left unharmed.
Scooby-Doo! Mystery Incorporated
Years later, the new Mystery Incorporated team followed up a clue in the diary of Cassidy Williams and also got into the place. Darrow mistook them for the old team and tried to trap and kill them. They only escaped through Fred Jones, Jr.'s expertise in traps. The ground around the building collapsed further, re-burying it and possibly destroying it completely. (Escape From Mystery Manor)