 The explored length of the cave increased from in 1952 to by 1968.It was the first cave in the world where the explored length reached 100 km, and until the linkage of the Flint Ridge Cave System to the Mammoth Cave System in 1972, it was believed to be the largest cave system in the world.Despite this, exploration of the Hölloch continued, and in 1976 it had been mapped to approximately long.