Entry No. 39 — the Des Moines file — filed under: only-highway-tunnel
Harmon Tunnel at Pammel State Park
The Harmon Tunnel is Iowa's only auto tunnel — a 150-foot passage hand-dug through a solid limestone ridge in 1858 as a mill-water chute, later widened for cars, where you actually drive your vehicle through the dark heart of the Devil's Backbone. The tunnel is still the primary road into the rest of Pammel State Park, so every visitor passes through it.
The move: Drive slowly through the tunnel together (roll the windows down to feel the cool limestone air and listen to the echo), then hike the Devil's Backbone trail above to look down at the ridge you just drove through — finish with a picnic on the Middle River bluffs at sunset.
📍 Before you go Pammel sits about four miles southwest of Winterset — head west on Highway 92, then south on County Road P68. You don't have to seek the tunnel out; it's the only road into the park, so you'll roll through it on the way in. The passage is two-way and narrow with pedestrian walkways, so creep along and watch for hikers. Spring through fall is best for the trails, the limestone bluffs, and the Middle River ford crossing (impassable in high water and closed in winter). Pair the trip with Winterset's Madison County covered bridges, the courthouse town square, and the John Wayne Birthplace Museum.
- 📍 Winterset
- 💸 Free
- ⚡ Up for anything
- 🌗 Outdoors
Where: 1900 Pammel Park Rd, Winterset, IA 50273
Hours: Mined 2026-06-07 — confirm current hours before you go.
Plan a visit & invite your people →
Further reading: khak.com · madisoncountyparks.org · notesoniowa.com
last checked: 2026-06-07