Books all have an ISBN. (This isn't something I've just found out, I knew that already).
They also have an EAN, which stands for International Article Number (originally "European Article Number", hence the abbreviation). My understanding of this bit isn't completely clear, but I think a book's EAN is its barcode number, and it has some of the same numbers as the ISBN but with extra little bits so that it can work as a barcode. (This is something I've just found out, but it isn't the interesting bit. The interesting bit is coming.)
There's a bit of an EAN that shows what country it's from.
When the EAN is for a book, the bit of the number that shows what country it's from says: Bookland.
This is not strictly speaking true any more, apparently the system changed in 2007 in a way that meant EANs can say 978 and mean "hey this is a book" rather than "hey this is an object and it's definitely from a country that we just made up". But if you grab a book nearby, one published before 2007, and look at the number on the back, that number says: this is an object, it comes from a place, and that place is Bookland.
How did I not know this? I don't know much about barcodes and EANs and ISANs and ISSNs and all the rest of it (I didn't know that EANs, ISANs or ISSNs even existed, until this morning). I admire them, certainly. miss_newham lets her secret barcode knowledge slip, occasionally, and I always think "yes, barcodes are pretty great!". But all the same, this is the single greatest fact in the world, and I only just found it out.
There's also a Musicland, for sheet music.