Henryton Tunnel
Henryton Tunnel, located near Henryton is the third-oldest tunnel in the world that remains in active railroad use. Constructed by the Baltimore and Ohio (B&O) Railroad and opened around 1850, it was the first tunnel constructed on the B&O's Old Main Line. In 1865 the tunnel was widened to accommodate double track. It was rebuilt into its current form in 1903. -from Wikipedia
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