There was a buzz going around Europe's occult underground in the early- to mid-seventeenth century that somebody uncovered an early draft of Shakespeare's The Tempest before it was edited for publication. (Although the references to it occur right around the time scholars think he wrote it, so it's entirely possible that the early draft started circulating in the occult underground before the play came out. Then again, it's not like these things are exact.)
Dukes who claim this story is true claim that the original play was less an allegory and more an occult history — the original Duke Prospero was a thinly-veiled Lodovico Lazzarelli, who instead of dying in 1500, retired to some weird island Otherspace that was supposed to be Avalon. (In this scheme, Sycorax was an immortal Morgan le Fay, served by a legion of Gypsy hardcases.)
Nobody knows what became of Lazzarelli or Morgan or anybody else — although some of the stories in Europe at that time suspect the House of Renunciation got to them first — but the crux of The Tempest is that Lazzarelli renounced magick and then left the island, leaving his library and artifacts (and Ariel, for that matter) behind.
Now I'll admit this whole thing sounds pretty sketchy, and maybe it's even a more recent hoax, but there's a little corroborating evidence — apparently somebody found some old plans written by Fausto Veranzio and commissioned by Louis XIII for a clockworker device to find the island. (Apparently, one of the plans was to incorporate Durandal in the design, operating on the belief that it's Excalibur and would sympathetically point to the place where it was forged.)
If we can find those plans, I bet we could hire Knezevic to build 'em. What do you think the odds are that the island is still there?