Could be Prunella, not sure about the species though,
around here grows a lot P vulgaris.

I believe that you are correct. Thank you for the information and tip in the correct direction. And to find out that this is actually the fabled Self-heal as well, what a surprise!

On a side note, I see that you are located in Switzerland. For Europe, is there a definitive hardineses zone map such as in the United States? Comparable to the USDA Hardiness Zone maps of North America. I enquire, because in the not too distant future of 10 years, I may be moving to Europe (most likely France or Switzerland).