It was not on my bingo card to see the Shell Grotto on HN.

I loved this place as a kid and would marvel at the patterns.

The air of mystery around who made it and why invites some fun speculation.

grottos were on recently - https://news.ycombinator.com/item?id=45809746

I'm about a mile from this right now.

The grotto is unpleasant - absolutely, in my opinion, a Victorian (give or take) rich man's folly, per the Wiki.

The imagery is all faux-Mediaeval - mostly the standard utter nonsense Rosicrucian 'interpretation' of Kabbalistic symbols. It's very bullshit, edgy, Hot-Topic-Victorian silly stuff.

Except for where, at the Malkuth mark, IIRC, it opens up into a sort of temple-and-altar situation, where it is actually somewhat frightening, in the way that any secret Bacchanalian temple is, because nobody builds that sort of thing for a good reason.

Extremely enjoyable place to visit. Unique and intriguing atmosphere within.

Why can’t someone do a carbon 14 datation of the shells to close the debate ?

I can think of several plausible reasons:

- it costs money and no one wants to pay,

- the mystery is more interesting or amusing than the resolution of the mystery,

- carbon dating is unreliable for dates following the industrial revolution because the burning of coal and oil ejected vast quantities of depleted carbon into the atmosphere.