We went through 2 tunnels during our Canal Barge Voyage on the Marne Rhine Canal.
The first was the Grand Tunnel D'Arzviller which was about 1.4 miles long. I think it took a half hour to travel through. All of these images are of this first longer tunnel, except for 12 which is the entrance to the second tunnel.
The second tunnel on the Marne Rhine we transited was the Petit Tunnel De Niderviller, about a third of a mile long. It took just over 10 minutes to travel through that tunnel.
Road Scholar French Canal Voyage By Barge: Discover Alsace-Lorraine Main Page