This card features an image of the underground lake that is a waterway for tourists, as indicated by the long flat boats with seating shown at the bottom of the image.
Color photo by W. Ray Scott and J. W. Young
The description states:
CRYSTAL LAKE IN MAMMOTH CAVE
Mammoth Cave National Park, Kentucky
The emerald green water of Crystal Lake provide a colorful contrast to golden tinted walls of the dome above the lake. Mammoth Cave is famous for its underground rivers and lakes.
— This card is one of the current series that dates from the 1950s.