A fun little afternoon trip with my wife, nephew and our dog (Oakley). The Narrows of the Harpeth Historic Area is the site of one of the oldest man-made tunnels in the United States. Around 1818, Montgomery Bell, one of Tennessee's earliest and foremost captains of industry, planned and constructed the 290 foot long tunnel through the limestone ridge at the Narrows to provide sufficient fall of water to operate an iron manufacturing operation at the tunnel's downstream side. Dug by slaves using black powder and hand tools, the tunnel at the Narrows is both a National Historic Landmark site and National Historic Engineering Landmark site.