In parts of Poland where I come from ( near Gniezno) one often heard about valuables being found burried in metal boxes. I remember as a child witnessing an incident where a crew diiging up a hole for a telegraph pole had found a large box full of silver cuttlery. Through decades of political turbulence and border shifts many people perished having hidden their private treasures in shallow ground. I wonder what the laws say about ownership of such finds today. Would any one know?
For now any treasure you would dig out belongs to the state, even something on your own property. Basicly what is under belongs to the state. Low remains unenforced most of the time but sometimes authorities would claim something offered for sale on ebay, allegro etc.
Some work is done to regulate it differently though - treasure hunters would get half of the value while the other half would be owned by the land owner.
In recent years there has been lots of people hunting and finding all kinds of things and media would sometimes inform on what was found and where if worthy their attention.