The Underground Booty SquadJust south of the west side tailraces is a low, flooded archway that leads back into an interesting drainage system. (Entrance is no longer accessible.) Just inside, the tunnel splits into two. The left fork dead-ends, but a hole in the ceiling takes you to a long, water-filled tunnel. At the end of this tunnel, a series of old, rusty ladders leads up four stories into the abandoned Gold Medal Flour mill - the only mill remaining on this side of the river. At the time that I explored it, this mill was not accessible by any other way.
At ground level, the ladders end and stairs await to take you further up into the plant. Several levels can be explored and each is different and interesting. About halfway to the top of the mill, a section of staircase has collapsed, leaving only the railing on one side as a dangerous but possible method of continuing to the top.
Unfortunately, this mill is being restored and will soon be turned into a museum.
Back at the first junction, the right fork leads deep under the center of Minneapolis, about 100 feet below the surface. Under the heart of downtown, there is a room with several catwalks that overlooks what explorers call the Raging River, or more technically, the NMT (North Minneapolis Tunnel), a large, fast-moving sewer that carries partially treated sewage from north Minneapolis to the sewage treatment plant in South St. Paul. Some adventurous explorers have taken a tumble down the NMT from the upstream end (see http://www.aberrant.org/~sand/drain/) to visit a bizarre, naturally-formed cave, Schiek's Cave, that is only accessible from this tunnel, and left downstream through this drain. (It's impossible to walk against the flow in there!)
A few blocks away, another cave in the sandstone is shown on a recent tunneling map, but we haven't looked for it yet.