Featured in the first two Harry Potter movies, home to the Duke and Duchess of Northumberland, and utterly deadly: welcome to the Poison Garden at Alnwick Castle! The Alnwick Garden was designed by Jacques and Peter Wirtz, lies in the rugged north of England and features more than 4,000 plant varieties. Visitors are not allowed to touch, smell, or pick any of the flowers (the most toxic blooms are kept in cages). A tunnel of ivy leading to the gardens. Many toxic plants are used for curative purposes, Bryonia dioica was traditionally used as a laxative. Be careful visiting that poisonous yet mysterious place!