Visitors to the Paw Paw Tunnel area of the Chesapeake & Ohio Canal National Historic Park in Western Maryland can see from one end of the 3,118-foot structure to the other -- although flashlights or headlamps are recommended for the darker middle sections.
The National Park Service maintains the C&O Canal, which follows the Potomac River for 184.5 miles from Washington to Cumberland.
The canal primarily hauled coal from Western Maryland to Georgetown from 1828 to 1924. Hundreds of original locks, lock houses and aqueducts remain.
The canal's nearly level towpath offers a trail through the scenic Potomac River Valley.
Construction of the Paw Paw Tunnel began in 1836, when Chesapeake & Ohio Canal Project engineer Lee Montgomery figured that building a tunnel through the Paw Paw Ridge of the Allegheny Mountains would shorten the waterway by six miles. His calculation that construction would take two years missed the mark -- by 12 years.
Montgomery's workers inched through the job at the dismally slow pace of 12 feet a week, using dynamite, picks and shovels.
Historic accounts relate frequent cave-ins, cholera outbreaks, unpaid wages and violence.
Montgomery's crews broke through in 1850, starting the flow of coal, farm goods and manufactured products until the canal closed because of more efficient transportation provided by highways and railways.
The construction feat of the tunnel, named after a fruit that grows in the area, seems paltry by modern standards: The Chunnel is 163,680 feet.
Today, visitors can stroll, hike or bike the towpath from the area's parking lot 0.6 of a mile to the entrance to the tunnel. The towpath follows a swampy stream where frogs communicate with guttural "thonk" sounds.
The path inside, lined with a sturdy wooden railing, follows one side of the tunnel, with the canal flowing below. Water drips down clammy walls. Voices echo off the 24-foot-high tunnel that contains 6 million bricks.
Fascinating rock formations dominate the view above the entrance to the tunnel.
Those rocks attracted geologists James L. and Danielle A. Stuby of Windsor Mill, who stopped at the tunnel after visiting friends in Cumberland.
"It's really beautiful," Danielle Stuby said. "I like going along the C&O to see such a neat old passage."
James Stuby, who was photographing rocks while looking for faults, explained that the rocks aren't horizontal because they were folded during the Appalachian formation. "I want to bike on [the canal] someday," he said.
Frank Stone of Virginia Beach, Va., has mastered that challenge. Stone, visiting with his wife, Paula; daughter Savannah, 9; son Stirling, 5; and dog Denali, said he "rode the C&O in the rain, though I walked in the canal. I went from D.C. to Cumberland on a bike."
Paula Stone also was fascinated by the geologic formations. "I love the rocks," she said.
The Lockhouse Restaurant, (11 E. Main St., Hancock, 301-678-6991). Sandwiches include the Canal Boat (crab cakes); entrees feature steak, seafood, chicken.
Panorama Steak House, (three miles west of Berkeley Springs on West Virginia Route 9, 304-258-9370). Prime rib, seafood, and a view of the Potomac River and three states.