The Yellow River Boardwalk Trail leads down the hill from the Effigy Mounds National Monument visitor center, through a tunnel under State Highway 76, through a riparian wetland, and onto a bridge that crosses the Yellow River. There are lovely views of the confluence of the Yellow River with the Mississippi River, and wildlife viewing is good as well. While there, we were entertained by a Red-headed Woodpecker (see iPhone photo) who almost seemed to purposefully greet and keep us company as we walked along the trail.
Completing the Yellow Boardwalk Trail earned an Effigy Mounds National Monument Hiking Challenge patch (See photo), celebrating the monument's 75th anniversary.