Picture of the "giant nest":
It's a creative idea, don't you think so?
If you are thinking that the tree house don't have windows, I can tell you that isn't true, the tree house have discreet windows that are hidden by the branches.
2 Pictures that show the discreet windows and the beds:
You can access "the giant nest" with the help of a retractable staircase, see the picture:
The creative tree house" was designed by Bertil Harstrom.
For more information (source): The Birg's Nest.