Map Transition by turning around

I have made a simple level with a small part of a house. I want to add the rest of the house as the player walks into a box collision in the room. However I don’t want it to seem noticeable for the character so they can just carry on moving around in a room and won’t notice that the rest of the house has been generated until they turn around. Does anyone know how to do this?

Level streaming using volumes:

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