Iowa has a unique tunnel, and it’s located in Pammel State Park near Winterset. It’s a historical treasure with an interesting history.

Harmon Tunnel is located in Pammel State Park at 1900 Pammel Park Road, Winterset.
Pammel State Park/Facebook
Google Maps
It's directly on state highway 92, just west of Winterset, and is the only highway tunnel in Iowa. It pierces the natural limestone ridge that is over 100 feet high and provides access to Pammel State Park.
The Pammel State Park area is heavily wooded, and the trails here are highly rated.
Jeff Westendorf/All Trails
If you decide to come to see the Harmon Tunnel, staying for a quick hike or a picnic is highly recommended.
The bridge was originally dug by William Harmon and his sons in 1858.
photolibrarian/Flickr
It was only a small chute designed to carry water diverted from Middle River to a saw mill. The original tunnel, designed to pass through the narrowest part of the horseshoe bend of bedrock was six feet high, six feed wide, and 100 feet long. In 1904 the mill was abandoned and the tunnel was expanded to allow vehicles to enter and exit safely, in 1925.
The tunnel has been expanded and reinforced further over the years.
Andy Langager/Flickr
It is now 100 feet long, 15 feet high, and 40 feet wide. It easily accommodates two-way traffic.

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Pammel State Park is a huge draw in the area. It's just 4 miles southwest of the town of Winterset.
Tim Baker Pammel State Park/Facebook
The tunnel is short, so cars can pass safely even with their headlights off.
Pammel State Park/Facebook
Sightlines are short both entering and leaving the park, so use caution.
Pammel State Park/Facebook
Some drivers even honk before they enter the tunnel as an extra safety precaution.
There are sidewalks along both sides of the tunnel's interior.
Pammel State Park/Facebook
Thousands of visitors hike the trails at Pammel State Park each year.
The area around the tunnel, and even the tunnel itself, is beautiful year-round.
Pammel State Park/Facebook
If you hike the trail that goes over the tunnel, you can see Middle River and miles of beautiful Iowa landscape.

Are there any other fascinating tunnels in Iowa that we should know about? Say so in the comments!

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