Treehotel owners Britta Jonsson Lindvall and Kent Lindvall enlisted six designers to create the 13-by-13-foot Mirrorcube, a reflective glass cube built around the trunk of a pine. It blends into the surrounding forest so well that the architects plan to cover it with a transparent ultraviolet film to alert flying birds, so they won't smash into it. Click here to see the interior and other modern tree house designs.  Modern Treehouses by Aileen Kwun from Swedish Treehouse Fantasy