Alnwick, United Kingdom
A run-of-the-mill treehouse simply won't do when you possess an English title. The Duchess of Northumberland commissioned this wonky structure, which opened in 2004, as a place for all the kids out there who "aren't allowed to climb trees." One of the world's largest treehouses, the elevated structure houses educational facilities, rope bridges, lots of walkways, and even a restaurant, and is made from sustainable resources. The design's whimsical angles and patchwork of materials is reminiscent of the world of Harry Potter—apropos, as the duchess's home, Alnwick Castle, was used as the location for Hogwarts School of Witchcraft and Wizardry in the first two films.