Ice Cavern in Antarctica. Photograph originally published in "The Heart of the Antarctic," Volume I, by E. H. Shackleton, 1909.
—Source: National Oceanic and Atmospheric Administration / Department of Commerce

Ice cave under Mendenhall Glacier, 1991.
—Source: National Oceanic and Atmospheric Administration / Department of Commerce. Photograph by Commander John Bortniak, NOAA Corps.

Ice cave under Mendenhall Glacier, 1991.
—Source: National Oceanic and Atmospheric Administration / Department of Commerce. Photograph by Commander John Bortniak, NOAA Corps.

Tunnel in Angel Glacier, Canada. This tunnel extends at least 100 meters into Angel Glacier.
—Source: Tom Lowell's Glacier Image Database, University of Cincinnati. Photograph by Doug McVey.

Ice cave in Iceland.
—Source: Tom Lowell's Glacier Image Database, University of Cincinnati.