Top 10 Cities for Urban Exploration

Minneapolis-St. Paul
Underneath the streets of St. Paul, a network of tunnels called the Labyrinth links abandoned and in-use sewer, phone and gas lines, among others. Lake County Museum/Getty Images

Big draw: The Labyrinth

"Tunnel system" would be a ridiculous understatement. Beneath the city of St. Paul, Minn., a massive, varied, nearly pristine world of interconnected tunnels reaches at least five stories deep and goes on for miles. Built in the 1800s in the heart of the city, it includes seven very different but ultimately connected systems, some overlapping in areas, some still in use, serving such varied utilities as phone systems, sewer systems, water and gas lines and power for the city's long-gone electric street cars. Each system reveals different architectural styles, with occasional carvings in the sandstone walls, presumably the work of those building the tunnels [source: Action Squad].

No one is allowed in. Access requires rappelling skills.

More to explore:

  • Ford Motors mining tunnels: Where the auto giant used to mine its own materials for glass.
  • Cambridge State Hospital: Infamous for abusing its mental patients.
  • Hamm's Brewery: Open from the 1860s to the 1990s, where beer-making equipment still remains [source: Action Squad].

Moving northeastward ...