I noticed these underneath a tree in front of our house a few years ago, and couldn't resist picking up a couple for the sheer weirdness of them! Then I saw they had some kind of nut inside, which I googled and found was a Turkish Hazelnut.
After a lot of effort with the nutcrackers (and some strategic turning to find it's weak spot) the very thick shell eventually cracked, revealing a lovely small fresh crunchy nut.
I foraged a fair few that year, then the following Autumn waited excitedly for them to start growing again. However, nothing appeared. Nor the next year. It seams they only bear nuts every few years, as they have once again grown in abundance this year.
I am now in a battle with a local squirrel to see who can stash the most away.
UPDATE: #HEYDIELINE Earth Month
10 hours ago