I looked it up on the internet when I got home (back to the RV, I mean!) and there's a nice write-up on St. Leo University and I also found some material on the grotto by googling that term. Apparently there are still pilgrimages to the grotto up to this day - the internet said several thousand people a year travel to visit it.
Pretty cool, huh? This is why I LOVE, LOVE, LOVE the AVA walks - there's no way in a thousand years I would have stumbled across this spot on my own. It's like finding treasure when an AVA wlalk leads you to such a surprising destination - and I think that's half of it, because I have absolutely no preconceived ideas about what to expect from these walks and sometimes they hold such delightful surprises!