These are both early shots of Natural Tunnel, near Duffield (sort of) in Virginia. This first one is an E.C. Kropp (Milwaukee) card. These people are obviously celebrating something. The sign on the red-topped building reads “Natural Tunnel”. There are no power poles visible. I would guess that the original picture (it was in black and white; the color was added at the printing company) dates to the first quarter of the 20th century. Note that the railroad is listed as “C.C. & O”.
This is a somewhat newer card, an Asheville Post Card Company issue. On the back: “The Natural Tunnel, located on U.S. Highway 23, 14 miles west of Gate City, Virginia, in Scott County, is said to be the only Natural Tunnel in the world used by a railroad. Through it the Southern Railroad has hauled many million tons of coal from the rich deposits of Southwest Virginia. (Kodachrome by Robert Suttle)”
Note that there are now power poles through the tunnel.