It seems most human societies have incorporated hallucinogenics in an official way, part of spirituality or rites-of-passage or medicine etc. When that stopped in our culture I'm not sure. [Facts and figures welcome.]
Personally, mushrooms are the best thing I've ever done. (Half a dozen times, in my 20s) Similar to LSD. Similar to religious enlightenment. Similar to... hmm well.
It's difficult to say anything that seems like it captures even 0.1% of the experience. It's like your brain can think 10000x faster, and also sideways, indexing items and memories by emotional content, meaning, in a way it couldn't before. And the flood of thoughts, images, emotions, can become so vivid and real that it seems real. Time disappears. You can experience in a minute what seems like it must have taken many hours ..But the experience isn't one thing, it's a thousand things.
I recommend it to everyone, especially with experienced/good friends to guide you the first time.