Eisriesenwelt, Natural ice cave in Werfen, Austria

The Eisriesenwelt is a limestone cave in the Hochkogel mountain of the Tennengebirge, above Tenneck in Salzburg. Its passages run 42 km, but only the first kilometre holds ice; the rest is bare limestone. The guided route passes the Posselt Tower stalagmite, the Great Ice Embankment, 25 m high, Hymir's Castle with Frigga's Veil, and ends at the Ice Palace, 400 m underground.

Anton Posselt, a high school teacher from Salzburg, systematically entered the cave in 1879 and documented his findings. Alexander von Mörk organized several expeditions between 1912 and 1913 that conducted cartographic work and expanded accessible areas. A cable car was installed in 1955 to facilitate visitor access after earlier tourists had to navigate a steep mountain trail.

The name Eisriesenwelt, "World of the Ice Giants", comes from Norse mythology: the tour passes Hymir's Castle, named after a giant, where stalactites form Frigga's Veil, the Ice Organ. Before Anton Posselt's 1879 exploration, locals knew the cave but believed it led to Hell and would not enter. Guides now light about five ice figures with magnesium lamps, and visitors carry LED replicas of carbide lamps.

Guided tours last 75 minutes and require warm clothing plus sturdy footwear, as interior temperatures remain constant at 32 degrees Fahrenheit (zero degrees Celsius). A cable car transports visitors from the valley to the cave entry point, followed by a 20-minute walk. Tours operate from May through October, with reservations recommended during summer months. Mobility is required for approximately 1,400 steps during the circuit.

The entrance portal measures 66 feet wide and 59 feet high (20 meters by 18 meters), creating natural wind currents that contribute to year-round ice formation. Scientists have determined that winter cold air circulates inside the cave and forms ice crystals when snow melts during spring. This air movement prevents summer melting in deeper chambers.