We have another person in this photo of the room styled the Chapel, presumably to add some point of reference for size and orientation. The image shows dramatic stalactites and more modest stalagmites throughout the image.

Photo by Diemer, Madison, Wisconsin

The description states:

Stalactites on the ceiling and dome-shaped stalagmites on the floor of the Chapel, Cave of the Mounds, Blue Mounds, Wisconsin

The woman’s attire indicates the photo is from the 1940’s.