The Underground Booty Squad
Named after three separate spiral staircases carrying water from the surface, this drain probably has the most notable design of any in the Twin Cities. If you follow it up about half a mile and turns down a small side passage, yet walking height, the first spiral staircase is found. The second spiral staircase is also at the end of a side passage, and the third, and largest, is at the end of the drain, about a mile and a half back from the entrance. All three spirals lead up about 80 feet to just below ground level. A walking-height tunnel leads both directions off of the top of the last staircase.
-Tunnelcity, 2004