This file is from Wikimedia Commons and may be used by other projects.
The description on its file description page there is shown below.
Summary
DescriptionSnail Shell Cave Karst Window.jpg
English: This is in the main entrance of Snail Shell Cave in Tennessee. It is a Karst Window entrance, where a collapse has occured into the middle of a cave stream passage. Here you are in one arm of the passage looking into the other arm. The cave extends for long distances each way with flotation required in much of it.
to share – to copy, distribute and transmit the work
to remix – to adapt the work
Under the following conditions:
attribution – You must give appropriate credit, provide a link to the licence, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
share alike – If you remix, transform, or build upon the material, you must distribute your contributions under the same or compatible licence as the original.