Related Clues:

• Escape route in "The Great Escape"
• Method of escape in "The Great Escape"
• Posh bishop and wife in eg New York underground
• Rapid transit option
• Zigzag by vehicle heading north in US rail system
• Underground in New York, say
• Subway passage
• Move around the Tube, essentially underground in America
• The American underground?
• Passage underground
• Mole's path