The Chesapeake & Ohio (C&O) Canal was once a means of commerce and a way of life for many. Construction began in 1828 and continued for 22 years. Running alongside the Potomac River from Georgetown (Washington D.C.) to Cumberland, Maryland, the canal was a transportation route for such goods as coal, lumber, and even farmers’ produce.
Nearly 185 miles long with a 608 ft. gradual climb, the C&O Canal consisted of lift locks, aqueducts, culverts, and even a 3,118 ft. tunnel—the Paw Paw Tunnel—which cut through the mountains, shaving off five miles of travel around a challenging bend in the river. The canal, which incidentally played a part in the American Civil War, had reached its heyday by the mid 1870s and ceased operations altogether in 1924. 
Today, the C&O Canal is a national historical park operated by the National Park Service.
The C&O Canal is unique in that it remains virtually unbroken and without substantial modification affecting its original character for its entire length of 185 miles. 
We set out last Saturday afternoon along the C&O Canal towpath where Fifteen Mile Creek joins up with the Potomac River near Little Orleans, Maryland. Our destination: Indigo Tunnel.
This stretch of towpath was once part of my Dad’s “beat” when he worked for the National Park Service maintaining portions of the canal a few years back. He’d seen the tunnel plenty of times before. It would be a first for my Mom, sister, nephew, and me.
Dad pointed out the old Western Maryland railway bed, built in 1904, which runs parallel to the canal. The rails close proximity, coupled with devastation by local flooding, eventually put the waterway out of business. But the old Western Maryland soon met a fate of its own. In 1975, the rail was abandoned when Western Maryland merged with the C&O and B&O railroads as part of the Chessie System (now CSX). The “new” rail is well within earshot on the other side of the Potomac. As we walked, we could hear the persistent whistle blows and clickity-clack of the tracks.
We eventually reached the vicinity of the tunnel’s west entrance, which is roughly a mile from the 15 Mile Creek parking area. Although it’s not clearly visible from the towpath, you’ll know you’ve reached the tunnel’s opening when the old railway bed starts to turn away from the canal, and the mountain becomes more prominent. (This is one of the few places where the old rail separates from the canal route.)
My Dad, nephew and I scurried across the canal, (the bed was dry there), and up the hill to the abandoned railway bed.
There it was. The Indigo Tunnel. I was thrilled!
“We can see it!” I called over to my Mom and my sister, who had stayed behind on the towpath.
Bats live inside the abandoned tunnel these days. Eight different species of bats, in fact. These include the Maryland state-endangered small-footed myotis, as well as the federally-endangered Indiana bat.The Maryland Department of Natural Resources considers the Indigo Tunnel one of the largest bat hibernacula in the state. As a result, the tunnel is closed to the public—barred with “bat gates”—to protect the colonies from intrusion and disease.
We heard the flutter of wings. Dad pointed out a bat, but it was gone before my nephew and I could distinguish it from the dark shadows. The smell of creosote, used to treat the railroad timbers, assailed our noses. All was silent as we gazed across the 4,350 ft. span to the light at the other end of the tunnel.
Hard work went into building the canal, laying the rails, and carving tunnels like Indigo and Paw Paw out of the mountains. The fruit of such labor was profitable for a season; but now the canal, the rails, and the tunnels are remnants of yesteryear. The “Grand Old Ditch” (the canal) still dips and bends, but runs mostly shallow to completely dry. The upper ridge bears faint and rustic reminders of the Western Maryland rail. And the Indigo Tunnel has been transformed into a bat cave.