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tunnel city usa 
Underground exploration in the Twin Cities Tunnels, drains, caves, and more
Together, Minneapolis and St. Paul make up one of the top two cities in North America in terms of the extent and variety of their underground spaces. New Yorkers will claim that their underground can beat Minneapolis by a long shot, and I've heard rumors of seven levels of tunnels and miles of water tunnels that connect different parts of the city. But others say that these rumors are unfounded. Who knows.
For the amount and diversity of the tunnels, the Twin Cities underground is virtually unknown. Many local residents are familiar with the numerous obvious caves along the bluff in Lilydale Park, but few know that there are seven different unique tunnel systems running under the same part of downtown St. Paul.
Why Minneapolis?
Minneapolis and St. Paul are built on the soft St. Peter sandstone, which is capped by a layer of solid Platteville limestone. The sandstone is easy to dig through, even by hand, and the limestone is at a good elevation to be used as a ceiling for caves and underground spaces.
As you will notice on the image below, practically all of the underground places in the Twin Cities are found along the Mississippi River between St. Anthony Falls in downtown Minneapolis and the east side of St. Paul. In this region, the Mississippi is bordered by tall cliffs, the bottom part of which are ideal places to dig level tunnels directly into the sandstone. Outside of this area, there are relatively few underground tunnels, because the surrounding land is relatively flat and the sandstone bedrock only extends a few miles beyond the city limits. Also, the thick limestone caprock away from the river makes it impracticable to dig down to the sandstone.
Click on the map for a description of each place, or click here to start at the upstream end and work your way downstream. Pictures coming soon!

Legend
So
far, only the Labyrinth has maps -- detailed and updated with every system shown.
Currently there are no pics on the site, but I'm hoping to add some soon. A
map of the West 7th Sewer Labyrinth will be added shortly.
Many storm drains are not shown because they are small or do not have significant special features.
Links
Action Squad: Premier group of adventurers from Minneapolis. These guys have been to almost every place featured here and more. Not only trip reports, descriptions, and pictures, but historical info and maps.
Minneapolis Drain Archive: Hardcore adventure group that uses a wide range of gear and techniques, including canoeing into drains.
Zone Tour: Group of French "cataphiles" that explore all the places under Paris, most notably the well-known "catacombs", telephone tunnels, high voltage galleries.
urbanexplorers.net: The underground info exchange, with information on numerous college steam tunnels in most states.
Infiltration: The zine about going places you're not supposed to go. Tips for exploring a wide variety of off-limits places.
Cave Clan: Large group of Australian urban explorers, with groups in each of Australia's major cities.
More links coming in the next few days. Check back for updates.