# Dungeon level
In NetHack, the dungeon level or depth represents how many levels you are beneath the surface. The dungeon level is closely related to a different number, level difficulty. Normally this is the same as the dungeon level, but has a few special cases:

In branches such as Sokoban that go upwards, the level difficulty increases as depth decreases. For instance, if the stairway to Sokoban is on dungeon level 9, the first level of Sokoban will have a level difficulty of 10, and the second will be 11, etc.
If you are carrying the Amulet of Yendor, level difficulty is the depth of the deepest level you have reached (which will always be the Sanctum in normal play).
If you are in the Planes, level difficulty is the depth of the Sanctum plus half your experience level. [1]
Contents

1 Effects of depth
2 Effects of level difficulty
3 See also
4 References

Effects of depth
Depth is shown in-game at the far left of the status line, as "Dlvl". You start the game on dungeon level 1, where it might read:

Dlvl:1  $:1699 HP:13(13) Pw:5(5) AC:8  Xp:1/0 T:1

Depth influences:

The number of gold pieces that generate in random piles and vaults.
Whether a shop square will generate a mimic instead of a real item.
Whether a mimic will appear as a strange object instead of successfully mimicking something else.
How many Keystone Kops show up when you rob a shop.
Whether closets will generate level teleporters and trap doors.
Whether a given room in the Dungeons of Doom will contain a random grave or graffiti.
Whether a given room in the Dungeons of Doom will be lit or dark.
Which types of special room a given Dungeons of Doom level is eligible for, and specifically the probability there will be a shop.
How much gold will be buried in stone.
Whether a level can have the Fort Ludios portal on it.
Whether a level will create bones if you die on it.
Effects of level difficulty
Level difficulty influences:

The monsters that are eligible to generate randomly, as well as which monsters are eligible to generate, when a single monster class is specified.
The experience level of generated monsters.
The number of gold pieces that generate in random piles, graves, containers, monsters' starting inventory, leprechaun halls, and treasure zoos.
Whether a randomly generated statue will contain a random spellbook.
Whether a water demon from a fountain will give you a wish instead of attacking.
The number of undead monsters appear when you raise the dead.
Which monsters are eligible to appear in a graveyard, throne room, or barracks.
Whether you succeed when you try to disarm a trap on a container or a trapped door.
The amount of damage an exploding door or tin does.
Whether a door will be trapped (or a mimic).
The amount of traps that appear in a given room in the Dungeons of Doom, and which kinds of trap are eligible.

The following information pertains to an upcoming version (NetHack 3.7.0). If this version is now released, please verify that it is still accurate, then update the page to incorporate this information.

Level difficulty also influences which themed rooms are eligible to generate, and sometimes also influences the contents of a room.
See also
Mazes of Menace, which outlines the list of levels in NetHack.
References

↑ src/dungeon.c in NetHack 3.6.6, line 1590