The Poison Garden at the Alnwick Garden in Northumberland, England, is home to more than 100 toxic, intoxicating and narcotic plants. And it’s open to public.

The sign on the black iron gate says, “These plants can kill”, and it’s emblazoned with a skull and crossbones for good measure. The warning isn’t a joke – the plot sealed off behind these black iron bars is the deadliest garden in the world. And it’s open to the public.
Established in 2005, the Poison Garden at the Alnwick Garden in Northumberland, England, is home to more than 100 toxic, intoxicating and narcotic plants. “Before visitors are allowed to enter, they must have a safety briefing,” said Dean Smith, a guide at the Poison Garden. Visitors are instructed that they’re not allowed to touch, taste or smell anything – nevertheless, as the website notes, guests have still occasionally fainted from inhaling toxic fumes as they walk through.
One of the dangerous plants cultivated here is monkshood, or wolf’s bane, which contains aconitine, a neurotoxin and cardio toxin. But that’s not the worst one: “Probably the most poisonous plant we actually have here is ricin [which contains the toxin ricin] better known as the castor bean or castor oil plant,” Smith said. “The Guinness Book of World Records considers that to be the world’s most poisonous plant.” 
Surprisingly, a lot of the things that grow in the garden are quite common. “Many of the plants in here do grow wild in the UK, and most of the plants are alarmingly easy to cultivate,” Smith said. Even popular home-garden bushes like rhododendrons are accounted for here. Those leaves contain grayanotoxin which will attack a person’s nervous system if eaten. “You’re not likely to eat the leaves, though, because they taste disgusting,” Smith said reassuringly.