These underground quarries, where primarily phosphated chalk was mined between 1877 and 1925, consist of a series of adjacent and sometimes interconnecting mines. The quarry covers an area of ​​nearly 68 hectares. Approximately 40 hectares of it can be accessed on foot or by canoe. The remainder is completely underwater or filled with chalky slime. This slime, cultivated in specially designed slime ponds, was used as a phosphoric-limestone amendment in the 1930s and 1940s.

These are therefore quarries, dug by human hands, and not natural caves. Moreover, there is no doubt about their age: the excavation of the galleries, which now cover over 175 kilometers, dates back to 1877. While similar quarries in the area had been exploited much earlier for the extraction of white chalk, the phosphated chalk extracted here was unsuitable for making lime and too fragile for use as a building material. Only when the first processes for chemically extracting phosphorus were developed in the mid-19th century did the importance of this chalk for the extraction of phosphorus (used in the production of fertilizers) become clear.

Large parts of the quarry are underwater. Depending on the amount of rainfall, the water level can fluctuate considerably. The limestone deposits give the water a distinctive blue color, giving the location its name 'Blue Lagoon'.