Related Clues:
- Prison escape route, perhaps
- Path for a mole
- Watching secretly
- 45-Down's activity
- Mine feature
- Holland or Lincoln, e.g.
- Underground passage
- An underground passage
- Passage through or under something
- Let nun turn in the passage
- An underground route
- Underground passage for road or railway
- Passageway under something
- Passage below ground
- Did that looney Leonard come up by underground?