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Mendenhall Glacier, a 12-mile-long mass of ice in Juneau, Alaska, is a popular tourist attraction. Few visitors, however, see the the glacier from its most spectacular vantage point: inside it.

Rising global temperatures have caused the glacier to start melting—it has receded by about two miles since 1958. Water has carved caves into the interior, creating surreal, turquoise-toned worlds whose shapes are ever changing.

A trip to the Mendenhall ice caves requires an arduous journey—it involves a kayak ride or long hike, an ice climb, and faith that the melting caverns won't collapse in on you—but the incredible landscapes are a once-in-a-lifetime sight.

Visit Atlas Obscura for more on the Mendenhall ice caves.

Ice to see you:

• Eisriesenwelt in Austria is the world's largest ice cave
• The Big Four ice caves form during late July and August and remain visible until October
• Nigardsbreen's cave is more like an ice cathedral

Visit Atlas Obscura for more on the Mendenhall ice caves.