As bats continue to die off, St. Cloud plans to transform old sewer into bat cave Greg Stanley, Star Tribune Thousands of hibernating bats have survived Minnesota winters by holing up in one of St. Cloud's oldest stormwater tunnels. Built in the 1920s, the almost ornate brick-and-mortar sewer opens to a ravine that pours into the Mississippi River. But the tunnel has failed to keep up with the growth of the city. With all the new homes, roads, driveways and other paved places added over the last century, too much water is now being sent through it, drowning out any creatures that may be sheltering inside and eroding the ravine where it empties.