This is a very old photo from my archives taken in 2011. We call these flowers “Maiglöckchen” in German, meaning Maybells and they appear regularly at the beginning of May. I had them in my garden once. I do not know where they came from, probably a seed found its was or a piece of root, but they arrived and almost took over. After 4-5 years I noticed that they are spread everywhere and so I began the task of removing them, which was not easy.
Now 7 years later I still find a few in between that begin to grow. They spread with their underground roots. Even my neighbour has some in his garden from me, but he has not yet noticed and I will not tell him. They are also extremely poisonous. I think it is a custom for young men to give them to young ladies on Mayday, but I am not so sure.