rmf / gdn - holey rock

Many years ago I was given a number of "holey" rocks - this is one of the larger ones.

Looks like a limestone that has been home to some marine worms that drill tunnels to live in, but I've no idea where it was found (or even if the person who gave it to me had collected it in the first place).
A couple of the others would have made good loom or spinning weights.