This is an Acorn, an oak tree.
There are many types of them, but I don’t know which one, it looks like Chestnut Oak.
In childhood, we made people, animals, etc. out of these acorns.
They turned out very beautiful!
Your photo of this tree made me nostalgic...
Your photos are great!
And rest is even better!
We also made little figures but not from acorns (there were not many around) but from chestnuts. It was almost mandatory to do it very autumn ;)
And we ate chestnuts, we had a different "building material" 😊 😊