A mile and a half from the Calumet Trailhead at Sheridan Lake, the Flume Trail runs smack into the side of a mountain. At least it would, except for the tunnel that's been blasted though the dark rock. Reinforced with wooden planks in the late 1980s, the tunnel's gaping mouth was the stuff my childhood nightmares were made of. Today, I duck down and step into blackness. I slide one foot forward on a wood plank—a makeshift bridge over the precipitation that has pooled on the floor—and hear water lap against the walls. So much for childhood dreams: This tunnel still gives me the creeps. As my eyes begin to adjust to the darkness, my husband grabs my hand and leads me forward.

He, too, has childhood memories of this trail and offers anecdotes as we make plans to traverse the whole out-and-back trail in one day. It's an ambitious 22-mile trek, but we're bolstered by an early start and anxious to see the trail's end—for the first time. Each time we've started on this hike, we've walked a little farther. As kids, we barely had the energy in our little legs to make it to this first tunnel. As teenagers, we slogged past this point—a little more than two miles, one way—to a second tunnel. As adults, we have trekked a little farther each time we've tackled the route.

While we saw a handful of fellow hikers scattered on the first expanse of trail—the section that follows the Centennial Trail for about a mile along the lakeshore—we're alone now, except for the occasional white-tailed deer or bluebird. This route is designated a National Recreation Trail, making the historical route a protected entity only open to foot traffic. The path follows the gentle downhill grade of the old flume bed, meaning this hike is more of a stroll than a workout. The two tunnel passages are early highlights, but we also keep an eye out for ruins along the trail. It takes a while for our eyes to learn to spot the old flume, but the ramshackle remnants are still there, hidden in the overgrowth. Occasionally, we spot an old plank, dotted with rusted square-head nails, bleached gray-white by the sun, and covered with mint-green moss. We walk over what first appears to be a grassy ridge only to see it is actually a pile of carefully laid stones, leftovers from an old stabilizing wall. The hike meanders through aspen groves, ponderosa stands, and open meadows with fields of wild irises.

As it often does in the afternoon here, a soft rain starts to fall. We break for a picnic lunch on a rotted log, and Chris picks wildflowers to place in my wide-brimmed hat. This time, we've managed to traverse nearly the full length of the trail, but we decide to head back because I'm dreaming of roasted marshmallows around the campfire. On the way back to Sheridan Lake and our tent site, we stop to watch a tiny waterfall or smoke curling from a farmhouse's chimney. Mostly, we just talk about the past, the future—and we make plans to come back to this uncrowded piece of Americana again and again, and one day cover the entire distance.

Natasha Gardner is assistant editor of 5280. E-mail her at letters@5280.com.

If You Go

The trek from Denver to Sheridan Lake takes six hours by car. Travel north on I-25 for 215 miles. Take Exit 126 to U.S. 18 east toward Lusk, which will eventually move you across the Wyoming/South Dakota border. After 122 miles, turn onto South Dakota Highway 89, which merges after 15.5 miles with U.S. 385 to carry you north into the Black Hills. Follow U.S. 385 to Hill City. Six miles past Hill City, begin following signs for the Calumet Trailhead and the Flume Trail on the southeast side of Sheridan Lake.

Stay
Sheridan Lake Campground: 605-574-4402; www.recreation.gov
The Rocky Loop sites at the Sheridan Lake Campground are at the water's edge (you can even dock a small boat or canoe here), and while the drive-in campground boasts its fair share of rowdy RVers, the massive lots are big enough that you can often see your neighbors' campfires but not overhear their conversations. Backcountry camping along the Flume Trail is allowed, but most people simply set up base camp near the lake.

Hike
The Flume Trail: 605-673-9200; www.fs.fed.us/r2/blackhills; www.gorp.com
This 11-mile (one-way) trail is designated a National Recreation Trail, meaning that bikes and vehicles are verboten. The result is a tranquil and well-marked trail suitable for both families (turn around before everyone gets tired) and experienced hikers.