Do you want to hold a flashlight, Doug?

I'd be happy to do that.

If you hear a big splash behind you, it's only me.

Doug Harris and Kathy Weaver-Taylor are standing in tall muck boots

in front of what looks like a shrunken stone doorframe built into the side of a hill.

Going in.

Kathy crouches a little, careful not to hit her head, and steps inside.

Doug and I follow behind.

Anything swim around down in here?

I haven't seen anything today.

We make our way through a narrow hallway,

our feet sinking into a couple of inches of water pooled at the bottom.

You're almost there.

The hallway opens into a big stone dome,

stretching over 10 feet in diameter.

And except for the light beaming from Doug and Kathy's flashlights and a little bit of sunlight

coming in through the entrance, it's completely dark.

This is not a cave. It's not natural. It has been prepared.

In tribal tradition, these are known not as caves or chambers, but known as Hasonek.

I'm Abby Peralt, and this is Atlas Obscura, a daily celebration of the world's strange, incredible, and wondrous places.

Today, we're heading to what's now known as Upton, Massachusetts, to visit this Hasanek, or ceremonial stone chamber that

was built hundreds of years ago. When we come back, we're going to hear from the people

...