^It's not the humidity or dryness of the environment, but the temperature that makes it go stale. Bread becomes stale fastest at refrigerator temperatures. Bread doesn't stale because moisture is leaving it -- t's not drying out at all, the chemistry is just changing.
Then I guess it must also depend upon the particular bread, and whether or not you have sliced it. I have witnessed some bread tending to resist staleness longer than others. I also save the end piece/slice as a kind of "cap" on the end, which seems to help the cut end from going stale.