Built using more than six million bricks, the tunnel has been described as "the greatest engineering marvel along the Chesapeake & Ohio Canal National Historical Park.

"[2] Located at milepost 155.2, the tunnel served to eliminate six miles of canal and is credited with contributing to the economic success of nearby Cumberland, Maryland.

Due to the high cost and long delay in completing the tunnel, the construction ended at Cumberland, Maryland, falling short of the original plan to take it all the way to Pittsburgh.

The tunnel and towpath are now maintained for public use as part of the Chesapeake and Ohio Canal National Historical Park.

[5] At Paw Paw, the canal engineers had a quandary with no easy solutions: follow the river (with its cliffs which would have required crossing over to West Virginia (then part of Virginia), damming the river to make a slackwater, and hacking out from the cliffs on the Maryland side) or make a tunnel.

The newly appointed engineer, Charles B. Fisk, managed to convince the board of directors of a tunnel's superiority.

[7] More unfortunately, this caused ethnic tensions which exploded into violence in 1837 and 1838, specifically between the Irish and everyone else; rioters destroyed the tavern at Oldtown, burned shanties, and the like.

[14] The NPS started a two-phase construction project to fix the scaling of rock on the downstream tunnel approach in 2017.