The Kalkberg is an artificial elevation in the city of Cologne.

It is located on the outskirts of the city center in the northwest corner of the Kalk district on the border with the Buchforst district at the angle of the city highway and railroad tracks.
The elevation was created by backfilling waste from the nearby former Chemical Factory Kalk (CFK) in an elevated landfill.
According to the findings of the City of Cologne, the backfilling with production residues was stopped shortly before the first waste law came into force in 1972, which means that the Kalkberg is not subject to the regulations of the waste law, nor to the rules of the landfill ordinance, but only to the soil protection ordinance. In the environmental office of the city of Cologne, this area is recorded under the suspected contaminated site number AL 80206. (Source: Wikipedia)Magnesium, calcium, potassium and iron, zinc as well as alkaloids, flavonoids, coumarins, saponins, glutamic acid, oxalic acid, the sterol β-sitosterol and a mucilaginous substance (Mucilago).

To preserve the ingredients, especially vitamins, young twigs and plucked leaves and best freshly harvested and chopped into small pieces are used in salads and curd preparations. If the leaves are to be used cooked, it is sufficient to blanch them briefly or steam them in butter.
Source: Wikipedia.com