Mystery underground storage site

This morning, I went down to the lakefront to drink my coffee. When I went back, I spotted this hole in the ground that I had never seen:

When I bought this property last summer, it was overgrown with trees, and one of the trees was growing in front of the hole. I cut the trees down in autumn, but the winter snow quickly came after that and covered the hole with snow.

Now it’s spring, the snow has melted and I noticed the hole for the first time. I took a look inside but I didn’t see anything in particular:

So I dug it out - most of it anyway. It turned out to be a rather substantial red brick construction with wooden slats shoring up the inside. And I mean substantial: the brickwork was thick, solid and deep.

In fact, it’s was so substantial that I had to leave the lower levels of bricks in the ground because they’re frozen solid with ice - and probably have been for decades.

I dug up the brickwork and exposed the the inner wooden slats first:

Inside, I only found old hay. Nothing special in the hay…

However, under the hay, I found a false bottom. Under it, nothing but dirt that had collapsed into the space over time, pieces of glass from a clearly very old jar, but otherwise nothing of note.

Now I’ve reached a stone slab. I think that’s the bottom, but I’m not sure because the brickwork seems to extend further down. But I have to wait until the exposed ground thaws to remove them and be sure:

This is how much of the old bricks and wooden slats I managed to pull out of the ground before the frozen ground defeated me:

Whatever that storage space was for is a complete mystery to me. But here’s what’s even more mysterious: this whole thing sat at the lowest level of the lake - basically at the level of the lake when it’s frozen in the winter, or after a particularly warm summer. The rest of the year, at least a few weeks per year, it was underwater.

Who the hell works this hard to build a super-solid storage space out of bricks and shore it up with wooden slats under the waterline?

And what does one store in a storage space near a lake that’s regularly flooded anyway? What was the point of that thing?

The previous owner, who bought the land in the 60’s doesn’t know what it is either. So my best guess is, it was there before she and her late husband got here. And back then, the lake wasn’t managed and its level may have been considerably lower than it is now.

Still, that doesn’t explain what a storage space in front of a lake is in aid of, and why it was necessary to line the inside with hay to store whatever was stored in there. Nor does it explain why it had a false bottom.

This might seem pretty exciting to you and you might wonder why I post this on Dull Men’s Club. I mean, I did find a mystery box on my property and got to dig it up like I found a pirate’s treasure chest or something. But here’s the thing: I spent the afternoon digging frozen ground with a shovel, found nothing of value and I don’t know what I dug up. If that’s not dull… 🙂

If you have any idea what this thing could be, or could have been used for, I’d be curious to know.