In my last apartment one place I had put some shelves and also stacked books was underneath the breakfast bar. But the breakfast bar was on the other side of the kitchen sink, and because of clogged pipes elsewhere in my apartment building my sink had overflowed, and for some reason I didn't realize at first that some of it had gotten underneath the breakfast bar and had soaked the bottom books. By the time I discovered it they were heavily mildewed and the mildew had started to spread. I still haven't replaced all those books. *sniff*