A very small and dark crawl space that's only accessible via a very small gap from a dingy nasty space in the basement. Unless someone were to actually crawl into the space they'd never find you, if you hid behind something in the space.
Of course if you suffer from even mild claustrophobia you won't last long in there. I suspect there are a lot of bugs in there, and it gets quite cold in the winter and quite hot in the summer. Because it's dark you wouldn't even see any bugs approaching, and if you turned on a light you'd instantly give away your location if your seeker happened to be in the adjacent space.