It looks to me like Arum alpinum

Here is a link that might be useful: Arum alpinum

How about the anthirium, peace lily family. Is this an indoor plant? I just noticed your zone, nice and warm, so it could be an outside plant for you. The flower is distinctive a peace lily (Spathyphilium flower) which is also in the Anthirium family.
I cannot be sure though because the leaves look out of proportion to the one flower. Need a bigger photo, if possible.

Doesn't look quite like either. Definitely not a Spath, could be another species of Arum.

Looks like Zantedeschia aetheopica, commonly called Arum lily.

Dee

I don't know this plant but it is not Zantedeschia aethiopica or a Spathiphyllum. It looks like a white version of our native Arum maculatum, so I would go for an Arum id.

The OP is in Greece. There are apparently 14 native Arum species. Since it came in local forest soil it will likely not be an exotic.

Here is a link that might be useful: Arums of Greece

Thanks for all the feedback guys! All I can add after googling many images and observing my plant is that it does seem to be one of the 14 local species of Arum. Now that is narrowed down maybe I will track it down to species level, maybe with the help of the Aroid Society. Its definitely not a Spathiphyllum or Zantedeschia aethiopica. If it is any help to you the leaves are 12 cm (4.9") long and 7.5 cm (3") wide and the flower is 15 cm (6") long. I have also added two more images of the whole plant to my album, although the flower has started to wither�

Thanks for looking everyboby!

I have to agree that I was wrong. I finally realised I could click on the picture for a larger version....that helped. ;o)

Dee