A place that is moderately to extremely unkempt, like an apartment, where what is causing the mess is books piled on and/or in shelves, boxes, and whatever other materials the person has to store the books. The owner of the books may be either an avid book collector or have OCD or both.
Did you ever go to Robert's house? It's Bookistan: wall-to-wall books! You can't even get a shoehorn into the shelves!