Devil's Kettle is a waterfall area in northern Minnesota where I live. It's on the shore of Lake Superior. I've seen it for myself and find it very cool but rather disturbing.

The two rivers.
It appears average right here. It is, it's a normal river. It's a few miles from the shoreline. Right here, the river forks into two smaller rivers. The one on the right flows down the rocks and down into Lake Superior. The one on the left, however, flows into a "pothole". This pothole has been researched by scientists, and they can't find an end to it. They label it virtually bottomless, though people claim that it has an underground passage into the lake, which I find reasonable.

The pothole.
I feel like a tour guide but this interests me for some reason. What are your guy's thoughts on it?
I didn't take the pictures. Thanks to Google.