Adding the portals to the cabin is the final touch. The cabin is not rectangular, so you will have to rotate the portals to match the angle of the walls:
Press 7 on the NumPad to get the Top view.
In the Viewport shading menu on the 3D View header, select Wireframe shading.
Select Portal Window.001 that you set aside earlier.
Press R, Z, 90, and Enter.
Press G and use the mouse to move the portal next to the left side of the cabin. Press the LMB to release.
Use Ctrl + MMB and Shift + MMB to zoom in so that you see the portal and the portal holes on the left side as well.
Press G and use the mouse to get the portal aligned as closely as possible to the forward portal hole. Press the LMB to release the portal.
Zoom into ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month, and much more.