How would you create a transition between different maps or rooms like in Luigi's Mansion?

Hi, I am on a quest to know how to create the transitional fade-in effect used to switch between maps/rooms like in Luigi’s Mansion.

For those who don’t know the game or prefer a visual example: view this video:
Luigi's Mansion Walkthrough Part 1 - YouTube.

Here’s what I know of how the game makes the transition between rooms seem consistent:
The mansion’s interior and exteriors are loaded in the same scene. Just that the rooms are completely transparent or they are hidden prior to entering them. Upon entering a room, the room you are already fades behind as you as you open the door to said next room. Such is shown in the visual above, thus hiding the previous room during runtime.

As you might have guessed, I am using the 3d template.

I AM NOT DOING A LUIGI’S MANSION FANGAME; I’M JUST AIMING FOR A SIMILAR EFFECT!!

If any of you in the Unity Community know how to pull this effect off, please share your suggestions. Thank you in advance.

Hi @DragonQueenGames , did you manage to do it, could you help me to do the same?

Thank you!

Hi @DragonQueenGames , did you manage to do it, could you help me to do the same?

Thank you!