Melvin Keisterbaum's mansion was located adjacent to the Blake Mansion. Melvin Keisterbaum seemingly lived there by himself. He said he loved the mansion more than his own kids... if he had any.
It was of comparable size to Blake manor however it was not built on a waterfront. It is in the French chateau style.
Scooby-Doo! Mystery Incorporateed
Under the Dreamweaver's control he detonated a bomb in his own mansion, destroying it, and nearly injuring Mystery Incorporated.
Blake Manor and Keisterbaum Mansion