The inside dimensions are about a half to a third of the outside.
It has those "stepped" doors on the inside, a lot like the safe in the Dahlonega gold museum.
I've got the visual now.

A guy I work with said that the local safe company in town,(I know where they're at... can't remember their name), has a safe mover that literally grabs it and "walks" it up and down stairs. Like an appliance dolly on steroids with an electric motor.

Sounds like a no hassle way but I'm sure it ain't free!
rags