Via Dana DeMaster and Than Tibbets’ Twitter conversation, here is a map of a mysterious and unknown subterranean engineering feature in Saint Paul, Minnesota’s weirdest city in some ways. Here is your map. The “sand rock tunnels” are in yellow.

 

[.pdf is here.]

The initial query came from yet another West 7th Street rumor:

My neighbor was just explaining that our block is not directly connected to the sewer. He claims a large cave is under our street. The sewage runs into the cave and then the cave is connected to the sewer. #skeptical

— @Hecate@toot.comnunity (@danademaster) May 5, 2018

It turns out to be true. The explanation is thus:

Here’s an illustration from Teresa Boardman’s blog. That and many more oddities can be found in the links on Twitter.

They say that “s**t flows downhill”, and in Saint Paul that is literally the case.