- [Narrator] This incredible glacier,

located in Alaska, is a popular tourist destination.

But the best way to see it is from the inside.

(soft piano music)

Mendenhall Glacier is a 12-mile long glacier

in the Mendenhall Valley

in Alaska's Tongass National Forest.

The ice caves are the glacier's surreal interior.

Access to see these icy walls

are only available to the truly adventurous.

To see the ice caves requires a kayak trip,

an ice climb over the glacier,

and once you're inside, the faith

that the melting walls around you won't give away.

But this natural wonder is under threat.

The glacier has been retreating

incredibly quickly in recent years

due to warmer temperatures and rising sea levels.

It has receded by almost two miles since 1958.

But what remains is an utterly breathtaking fantasy land.

(soft piano music)

(techno beep)