StairCASE

Tall case and ladder/steps built into one. Check his site for a series of images that show it "working".

Personally, it is pretty clear that the bottom shelves would take "excessive" dust/dirt/debris as they are used as steps...but for a working/reading library, this might be a fun and efficient solution. It could also be "finished" in such as way as to avoid the pine box look shown here. 14 points for creativity.