The Stearn Mansion has been in the Stearn family for thousands of years. It is located on Slaughter Mountain, somewhere in America and is the home of the current Mr. Monster.
When Jim Stearn gave up his life as Mr. Monster to be with his wife Lillith Weiss, he moved out of Stearn Mansion. After his son Strongfort was born, Lillith abducted Strongfort and took him to Stearn Mansion to kill him. However, due to the intervention of Jim Stearn, both Lillith and Jim died there, instead of Strongfort.
The mansion contains a museum of all Mr. Monsters, collecting trophies, pictures, diaries and even bodies of slain monsters. Dracula, Lillith's father, is buried here as a trophy.
Underneath the Stearn Mansion lies a tunnel called Road To Eternity. It contains paintings of all Mr. Monsters, going back to the very first one. As soon as a Mr. Monster is slain in battle, his picture is added to the rest. The tunnel leads directly into the Judgement Chamber, a sacred place for the Stearns. It was in that chamber where Jim Stearn was encased in ice after the agreement with the Fluorescent Five to make him a Mr. Monster again to save his son from Lillith. After Strongfort forgave his father for almost ending the line of Mr. Monsters, Jim broke free from the ice, his soul finally leaving Earth, and his picture was added in the Road To Eternity.