St John's headquarters in Gonville is so overflowing with books that some have to be stored in a shipping container.
There's an entire storeroom filled with boxes of books; and boxes line the hallway, are stacked in corners and poke out from under tables.
So it's just as well that St John is having a book sale this week. The sale will be held from Thursday to Saturday, and will include a wide range of books, magazines, CDs, and games and puzzles.
Organiser Jenny Burkett said the task of organising and running the book sale was so big that it took 40 volunteers to get the job done.
"We are very lucky to have such enthusiastic volunteers. We've probably got hundreds of thousands, if not millions, of books here - but we can't sell them all in one sale."