This is a skybox of the old Bedroom interior. It essential makes it look you are inside the Bedroom and the Bedroom floor is infinite.
This was not made using the original interior. I modeled the Bedroom and textured it myself in a 3D modeling program and rendered the skybox using that. Because of this, this Bedroom does not look 100% identical to the actual one, but it is close enough that you will not really notice any differences.