Iron bars
Iron bars are a dungeon feature represented by #.
They are never randomly generated, save in SporkHack, and UnNetHack where they might replace doorways. There are iron bars in the Wizard, Tourist and Ranger quests.
You cannot walk through them, and objects thrown through them have a chance of being stopped by the iron bars. All monsters which are whirly, amorphous, phasing, tiny, or slithy and not large can pass through them,[1] including you if you are polymorphed into such a monster.
In SLASH'EM and UnNetHack, iron bars may be found in some of the new levels of Sokoban, and sometimes on maze levels. Creatures cannot pass through the bars in Sokoban; a Doppelganger character may still liquid leap through them, however. In UnNetHack, creatures are able to pass through Sokoban bars.
