The poison garden at Alnwick Garden in northern England is so dangerous that you can only enter it if accompanied by security personnel. Many of the plants are surprisingly poisonous.
As a precaution, you will always be accompanied by a tour guide during the walk, because the plants must not be touched or smelled. The poison grayanotoxin contained in its flowers and leaves has a hallucinogenic effect in small quantities, fatal in large ones. The castor bean tree's seeds are lethal even in the smallest quantities.