IO9, the science fiction blog that's part of the Gawker article, runs an interesting article on the Eleusinian Mysteries (or, as IO9 puts it, "The Psychedelic Cult That Thrived for Nearly 2,000 Years.")
Interesting sentences: "If you would like to check out a modern production of the Eleusinian Mysteries, the Aquarian Tabernacle Church uses the scant knowledge of the mysteries to recreate the known rituals every year around Easter during their Spring Mysteries Festival at the Fort Flagler State Park in Washington State. The ceremonies are open to anyone and provide a rare insight to one of the most popular societies of ancient Greece and Rome."
The Eleusinian Mysteries are mentioned a couple of times in ILLUMINATUS!
Anybody who wants to go to the trouble can find out, for instance, that the "secret" of the Eleusinian Mysteries was the words whispered to the novice after he got the magic mushroom: "Osiris is a black god!" (Page 123)
[amanita muscaria claimed as] the sacrament used in the Dionysian and Eleusinian mysteries in Greece (page 297).
Thanks to Rob Pugh, on Twitter, for the pointer.