Hölloch

The Hölloch is a karst cave system located in the municipality of Muotathal, Switzerland. It is notable for its immense size, ranking as the third longest cave in Europe and the eleventh longest in the world. The cave also possesses a significant depth. Scientific exploration of the Hölloch began in 1875 under the leadership of Alois Ulrich.

Later, in the 1950s, the speleologist Alfred Bögli, a pioneer in the field, led expeditions that successfully explored a substantial portion of the cave. The known length of the system grew dramatically over the following decades, increasing from a certain measurement in 1952 to a much greater length by 1968. During this period, the Hölloch became the first cave in the world to have its explored length reach 100 kilometers. Prior to the connection of the Flint Ridge Cave System to the Mammoth Cave System in 1972, the Hölloch was believed to be the largest cave system on Earth.

Exploration continued after this, and by 1976, the cave had been mapped to a length of approximately 130 kilometers. A small section of the cave near its entrance is open to tourists, but due to its enormous size and complexity, the rest of the system is accessible only to qualified cavers.