Level in a Level?

Is it possible, that in the middle of a level, you walk through a door, and it takes you to another level INSIDE that level? Or like, a secret level?

The obvious choice is to go to another layout, but you will lose the state of the main level. I would just expand the layout size, then make the chamber in the same layout and just teleport there and back.

Inception

I don't know what you are thinking to do, but if I'm correct you should make the first level and the second level at the same layout, but pick "At the start of Layout > Hide SECOND LEVEL" and "When player is overlapping the DOOR > Set visible SECOND LEVEL".