My recollection, too, is that the story dealt with the author of the Akdomus.
Wolf: Just because they can’t find it today does not mean it doesn’t exist. They are constantly finding the existence of people that they did not previously know existed. Obviously the 10 shevotim exist somewhere too.
Lastly, I seem to recall that there was a gadol (I believe it may have been the Rambam or the Ramban), about whom it was said that he had a jar of the Sambatyon water in his home that bubbled and churned all week but became calm on Shabbos. Imagine the affect that would have on anyone who may question the existence of a creator that rested on the 7th day!