Impossibe Map Design?

I’m trying to create a level in my game where there is a door in the center of the room. You can walk around the door frame and you can also go through the door to enter a second room. From the first room you can see into the second room if you look through the door way. Does anyone have any idea how I might do this or even what this is called so that I might be able to learn how to do this.

Take a look at Render Textures. As @cdrandin noted, this is a Unity Pro feature.