The heart of downtown exploration in Minneapolis is the Washington Avenue Drain system. Built in the 1930s to provide sewer and stormwater separation, these drains underlie the core streets of downtown and outfall to the river in the former tailrace canal of Mill Ruins Park. Near the outfall is an impressive brick arch room, and two former sewer tunnels leading south towards the trunk sewer interceptor known as the North Minneapolis Tunnel. This sewer used to flow directly into the Mississippi, but is now diverted towards St. Paul's treatment plant. The NMT is still accessible at a regulator structure beneath Portland Ave, but this may soon change as a major construction project threatens to completely separate the drain and sewers. This drain can flood to the ceiling and beyond during heavy rain, as evidenced by the occasional deep gravel bars, rocks and concrete chunks washed downstream, and pressurized water reaching street level 90ft above. In a few places the drain has begun to decay from storm damage and flooding, sometimes leaving broken access hatches or holes in the walls and ceiling leading to construction voids and overbreakage caves. Unfortunately, the Minneapolis underground appears to be much less complex and tunnel-endowed than St. Paul's city center, and will likely bore the casual spelunker with endless identical concrete walls and boring side tunnels.

The other main tunnels found under Minneapolis are the NMT and it's tributaries. These are almost always topped by hexagonal manhole lids 90ft up on the surface, and can be identified by their bad smell and fast-moving currents of poop. Since most Minneapolis tunnels are lined with brick, stone, or concrete rather than bare sandstone, there are few rats and few opportunities for interesting cave connections.
 

        
Some views from the regulator construction project. The first two show the place where drain and sewer pass eachother, the middle photo shows the "Raging River" of the NMT, and the last shows a huge blue air filter. This site has changed significantly during the year, and could eventually seal off the NMT from the drain completely. Also found in this area are a backfilled TCRT power tunnel and a sewer tunnel serving the former milling district and once connected to the tailraces (Known as the Rat Tunnel).

  
Some typical cross-sections of this tunnel system, and a simplified plan of the regulator. Lowering the gates theoretically diverts the sewage up and over into the drain outfall, although the gates used to be far too rusty to actually work.

      
The other major tunnel beneath downtown is the New Bassett / 2nd Ave Tunnel, carrying Bassett Creek under the city and outfalling very close to the Washington Avenue drains. This is the "Canoe Tunnel" mentioned by Peter Sand. The outfall and infall are both nearly impossible to enter safely, the former being submerged and the latter leading to a 30ft waterfall. The only safe access is far up a side branch and involves a long walk through cold fast-moving water.

Some cross-sections of the New Bassett Drain.

  
Bassett Creek used to flow through a large tunnel dating from the late 19th century. This tunnel is still used as a drain, but is largely abandoned. I plan to explore this one when I have more time.

            
This short but confusing system is known as the Frylunt drain after two of it's discoverers. Another 19th century sewer outfall, Frylunt passes beneath the U of M's West Bank campus a short distance before dead-ending at a dropshaft. Two shafts midway down the drain lead to upper level sewer tunnels, one completely abandoned (first and 2nd photos) and one split in half to accomodate both sewage and stormwater (middle photo). There used to be a large natural flowstone formation in one of the side tunnels, but it was recently destroyed by Minneapolis Public Works wankers.
 

         
An interesting but very small and back-pain-inducing drain under downtown. This one is another former sewer, and isn't too great.

  
This is what happens when you have poor data on tunnel locations and think you've found something totally St. Paul Style under MPLS. A stealty midnight rappel down a secluded hex lid ends in just another NMT side branch and a lot of smelly rope.

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