Beneath the grated walkways at your feet runs the hydraulic tunnel system that powered the most productive flour-milling district the world had ever seen. Mill Ruins Park preserves the stone foundations, tail races, and tunnel entrances of the flour mills that operated along this stretch of the Mississippi from the 1820s through the middle of the twentieth century. The Dakota people called the falls Owamniyomni — the whirlpool — and they were sacred ground long before European settlers arrived.
The first sawmill opened here in 1823, powered by the falls. By the 1880s the west bank was wall-to-wall mills: Washburn, Pillsbury, Crosby, Gold Medal. The tunnel system you see below ground channeled water from the head of the falls through underground passages to turn turbines inside the mills, then discharged it into the tail race and back into the river.
The city has excavated portions of the tunnel for walking tours — if they're available today, take one. It is disorienting and extraordinary to walk inside the hidden infrastructure of the flour capital of the world.