August 3
Deep inside the Tennengebirge mountains lies a frozen world.

The Eisriesenwelt ice caves at Werfen near the Austrian city of Salzburg are said to be the largest in the world.

But the ice in the Eisriesenwelt ("World of the Ice Giants") has actually grown by a third since the 1920s.

And there has been a marked increase in the growth of ice over the past 15 to 20 years.

The warmer temperatures on top of the mountains may be helping the formations to develop earlier than usual.

Only a few caves in the Alps are filled with ice

The ice is formed by water seeping through crevices into the freezing caverns below.

The sooner the snow melts, the earlier water starts dripping into the caves.

One of the first ice structures you see after entering the cave did not exist 10 years ago.

The huge pillar was formed by tiny drops of melted snow water trickling through fissures in the rock.

Even in the height of summer, temperatures in the caves usually stay below freezing.

There are thousands of caves in the Alps - but only a handful of them are filled with ice. Ice caves require special conditions, with at least two different openings at different levels.

Most of them are found at a height between 1,300 and 2,000 metres (4,290-6,600 ft) above sea level.

So far it seems that warmer temperatures outside have been beneficial for the ice caves.

In the heart of the ice cave, a row of icicles forms a sculpture known as Frigga's Veil, named after the ancient Norse goddess of the heavens.
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