A school principal who wanted to clear out his bookshelves has created a game that’s attracted nearly 50,000 people. Belgium’s Aveline Gregoire says he was inspired to create the “Book hunters” game by the success of Pokemon Go.

Unlike the Pokemon game, the book hunting game (known locally as “Chasseurs de livres”) doesn’t use GPS or cameras. Instead it’s simply a Facebook-based treasure hunt. The idea is that players who finish reading a book hide it somewhere (usually in a protective cover) and post a photo and hints about where to find it.

At the time of writing, 46,815 people had joined the Facebook group, though it’s unclear how many are actively hunting books. It is clear the game has spread far beyond Gregoire’s home town and includes many more books than he originally “released.” Gregoire told Reuters that he’s considering developing a dedicated app for the game.

Even for those who don’t join in, the group’s welcome page has some excellent advice even in auto-translated form:

And above all, and in all circumstances, we stay zen, we keep the smile and we don’t take the head.