The Fly Agaric Amanita muscaria is the famous white-spotted red toadstool beloved of children's book illustrators.
They are widely known as one of the few poisonous fungi in the UK, but it is not generally realised that this is because they are in fact strongly psychedelic. Eaten raw, they cause stomach cramps, hallucinations* and, possibly, death.
In some parts of Europe they have long been associated with magic and legend. In Lapland, reindeer regularly get high on them and are seen to leap around, giving rise to the story of Santa's flying reindeer. Lapps have a custom of deliberately feeding them to their deer, and then collecting and drinking the urine because most of the toxins are filtered out by the reindeer's digestive system.