Corridor
Corridors, represented by # (or # if lit, or ▒ (unlit) and ▓ (lit) with IBMgraphics ), are passageways connecting rooms in the Dungeons of Doom and Minetown. Not all corridors lead to rooms, and many have hidden sections (called a secret passage) which must be located by searching. Others may have boulders blocking your path. It is never impossible to progress further in the dungeon. If you come to a dead end, search all the walls until you find a secret passage. If a boulder is blocking your path, either destroy it (if you can) or drop everything you have so you can squeeze by the boulder and try to push it to a better location.
Corridors are usually single file and always unlit. Telepathy, Warning or Infravision are helpful when walking in corridors.
Gehennom and Sokoban also have passageways and single file routes. However these are the level itself, rather than connecting rooms.
With the exception of death drops and the occasional scroll of teleportation, there is no loot in corridors, but mercifully the only traps are from ad aerarium or 'Vlad was here' closets.
Strategy
Advantages
Corridors are usually single file, so you are less likely to be overwhelmed by numbers alone. Also, since they are only one tile wide, enemies are lined up for convenient disposal by wands, spells or ranged attacks.
If you are overwhelmed by a long column of enemies you can displace your pet and switch places with it for a few turns so you can recuperate.
Disadvantages
The darkness means you have difficulty locating enemies without telepathy, warning or infravision. This is a bigger problem for those roles relying on ranged attacks. A light source can helps you avoid monsters, but it also helps enemies find you. Monsters can also block off your path, including slow-moving monsters such as gas spores and floating eyes.
Tips
Move diagonally past corners to save time and get around faster. Corridors end when you find a door. If you are on an early level be sure a locked door isn't a shop door (there will be an engraving, "Closed for inventory"), before you kick it down. If the corridor ends and there is no door, there is likely a secret door nearby.
Use a light source if you can spare it to avoid any awkward encounters. A light spell is particularly useful since it is permanent.
See if you can establish a circuit, a series of rooms and corridors you can circle around indefinitely to hold off and kill monsters which are as slow or slower but more powerful than you (by running in a circle you will regain HP and Power over time). See hit and run.
Creation of Corridors
You can create corridors yourself with the aid of a pick-axe, dwarvish mattock, dig spell, wand of digging or polymorphing into a rock mole or umber hulk. If you find large amounts of rocks, gems or gold in a corridor this is a sign it has been dug by a monster. Always think of the possibility of a bones file character.
In particular, without a means of teleportation you need this ability to reach a Vault, a 2x2 room filled with gold.
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