Last August, a camera crew went underground beneath Forest Park and found something most St. Louisans have walked over their entire lives without knowing about.

More than thirty feet below the ground in Forest Park sits a system of tunnels that are part of the River Des Peres, where over four miles of its nearly ten-mile path sit beneath the city. You are walking above a river right now and you don’t know it. That’s the whole story, really. Everything else is just details.

The tunnel is technically the modern-day River Des Peres, which was first moved underground prior to the 1904 World’s Fair to help with flood control. After the fair, it was brought back up, only to be buried again nearly twenty years later. The reason it was buried the first time: it had become an open sewer. The city was growing fast, wastewater treatment didn’t exist yet, and the river was collecting everything that people didn’t want to think about. Right before millions of fairgoers arrived to see the future, they put the river underground and pretended it wasn’t there.

They’ve basically been pretending ever since.

A public historian with the Missouri History Museum called it “history hiding where you don’t expect it.” That’s a polite way of saying the city buried a river a hundred years ago and told almost no one.

The tunnels are locked. They fill with water in minutes during a storm. You are not supposed to go down there. But it’s there, moving quietly under the joggers and the art museum and the sculpture garden, going wherever it goes.