Door to new Scene

I recently tried out this Unity game called “These Monsters” (link below) which features procedurally generated islands. On each island is a structure with several doors. The doors all lead to different islands, and I was wondering if anyone could explain how these doors work. They work like the doors in Monsters Inc. When the player walks up to the door, it opens automatically and shows the new island on the other side. The player can then walk through the door seamlessly into the new scene. Does anyone know how this is done? How does the game display a different scene through the door?

Here is a video of someone walking through one of these doors. They walk through a door at 1:46:

Here is a link to the game:
https://strangethink.itch.io/these-monsters

To try to make this simple think minecraft alittle everything is procedural generation …

So when he is looking at the "two scenes " the camera and player distance are actually generating based on field of view… so when it looks like there are different dimensions it’s actually recuculating the map to cut off and generate.

I have no easy script for this because it would take months to get something solid like this … but I would go to research procedural generation based on a camera view and go from there.