This was found on the beach in Romania (Black Sea). It is about 6cm. I have no idea what it is.
At first look it seems like a fossilized coral. But as I did some research, this doesn't really look like other fossilized corals I've seen. Another option could be borings made by creatures, but a lot of them are openings rather than holes (apart from a big deep hole which is visible in pictures, is that a boring?). Another option I found is something volcanic, but why does it have so many holes? Any help is greatly appreciated, thank you!