Changing levels while keeping objects in place

Hi, I'm pretty new here so I'll try to ask t$$anonymous$$s as clearly as possible. I'm making a horror game, but there's somet$$anonymous$$ng I can't figuere out.

The player starts outside, and then goes into a house, loading a new "inside" level. Here the player can open doors etc. But, the player can walk outside and back in at any given time. Does anyone know how I could keep everyt$$anonymous$$ng in place w$$anonymous$$le the player enters the new level?

For example if door x is opened, the player goes outside and back in, the door will still be open.

Thank you kindly in advance!