Hidden just outside Juneau in Alaska, United States, the Mendenhall Glacier feels almost unreal, inside and out. Step into one of its rare blue ice caves, and the world turns quiet and luminous, with light filtering through centuries-old compacted ice. The glacier stretches about 13 miles from the Juneau Icefield, slowly flowing toward the valley below and reshaping itself year by year.

Its striking blue colour comes from the ice's density, which absorbs most wavelengths of light and leaves behind vivid shades of blue. These caves are fleeting by nature, forming as meltwater carves tunnels through the glacier and disappearing, or collapsing entirely, as conditions shift.

While reaching the caves has become increasingly rare and unpredictable, the glacier remains closely studied and deeply admired. Over the past century, it has retreated dramatically, offering scientists a visible record of environmental change. Inside these glowing chambers, beauty and fragility meet, creating a powerful reminder of how dynamic and temporary Alaska's frozen landscapes truly are.