# Level teleport
To level teleport (or levelport) is to teleport to another level (as opposed to somewhere else on the current level).  This is dangerous without teleport control, as it can deposit you just about anywhere, including below the point you are equipped to handle safely, but with teleport control it is an incredibly useful tool.
When arriving at a level by means of levelporting, you are placed randomly on the level, unless the teleport region is restricted in the special level file. 
Level teleportation can be achieved by:

reading a cursed scroll of teleportation
reading a scroll of teleportation of any beatitude while confused
stepping on a level teleport trap
#invoking the Orb of Fate
Uncontrolled level teleportation will deposit you on any level between 1 and your current level plus 3, except that you will not go below your current dungeon branch.[1] There is a 20% chance you will stay in place; otherwise, all other eligible levels are equally likely.[2] This is helpful when you need to travel up. 
Level teleport for monsters works the same way and is always uncontrolled.[3] If your pet steps onto a levelporter, you may have a hard time finding it again. Telepathy, a magic whistle, or a monster detection can help in locating it, but they only work on the current level.
Assuming you have teleport control, if you attempt to teleport to a level below Moloch's Sanctum while in Gehennom, you will instead be teleported to the vibrating square level (or the sanctum, if you performed the invocation already), which can be useful if you choose to explore Gehennom bottom-up. You can attempt to teleport to levels above 1 as well, although they generally end the game, so they're only good for a few YAFMs.
Monsters which follow you on stairs will also follow you when you levelport.

Contents

1 Restrictions
2 Messages
3 See also
4 References

Restrictions
You cannot levelport from above the Valley of the Dead to below it; you will end up in the Valley instead. You can levelport from below the Valley to above it, and may levelport into the Valley from any level, or to any level from the Valley.
You can levelport out of your current dungeon branch if you are going upwards (e.g. from the Gnomish Mines to the level where they branch off the Dungeons of Doom or any shallower level), but not down (e.g. from Vlad's Tower to Gehennom).
You cannot levelport in Sokoban.
You cannot levelport from or into Fort Ludios.
The Quest branch has its own separate level numbers. You cannot levelport into or out of the Quest branch, and any controlled levelport inside the branch uses the Quest level numbers (so "1" is the Home level and "3" is the Locate level, even if the Quest portal is on level 14). You cannot levelport below level 1 until you have permission to begin the Quest.
You cannot levelport into Moloch's Sanctum until you perform the Invocation. However, once you have performed the invocation ritual, you can levelport in without having visited the Sanctum; this will place you near the upstairs.
You cannot levelport while carrying the real Amulet of Yendor (though you may still quaff cursed potions of gain level).
You cannot levelport in the Planes, except in wizard mode. Even in wizard mode, you can only levelport to the next or further Planes, never backwards.
Controlled levelporting to level 0 will kill you, but an amulet of life saving can save your life. The game will ask for confirmation before you do this.
Controlled levelporting to a negative level will irretrievably end the game: If you have any of levitation, flight, or life saving, you escape; otherwise, you die. In either case, the game will not ask for confirmation before you do this.
You cannot enter the Wizard's Tower by levelporting. However, if you are already inside and your target level is one of the three tower levels, you will stay inside. This is useful if you wish to bypass the zoo. You can also teleport from inside the Tower to non-Tower levels above or below it.
There are various squares that you cannot land on by levelporting. On most levels, only rooms and air are legal arrival locations; on maze levels, corridors are also legal arrival locations.[4] Additionally, you cannot land on a trap.
Gaining a "dungeon level" from a cursed potion of gain level has similar restrictions, except that the Amulet of Yendor&nbsp;does not block it, and it does not let you leave the Wizard's Tower.[5] Quaffing it on dungeon level 1 on the ascension run is therefore a safe way to enter the Planes if you are not sure if your Amulet of Yendor is a fake.
Monsters are subject to the same restrictions, except they can levelport in Sokoban and the Quest, and they cannot successfully use a cursed potion of gain level when in Sokoban or carrying the Amulet.

Messages

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.

The following message is new in 3.7.0.
You materialize on a different level!
You levelported.
Go to Nowhere.  Are you sure? [ynq]
You are attempting a controlled level teleport to level 0.
You scream in agony as your body begins to warp...
You cease to exist.  Your possessions land on the floor with a thud.
You confirmed you wanted to teleport to level 0. Your death is recorded as "committed suicide".
An energized cloud of dust begins to coalesce.
Your body rematerializes, and you gather up all your possessions.
As above, but you were wearing an amulet of life saving.
You are now high above the clouds...
You performed a controlled levelport to levels −1 through −8.
You feel deliriously happy.   (In fact, you're on Cloud 9!)
As above, but the controlled levelport was to level −9.
Unfortunately, you don't know how to fly.
You plummet a few thousand feet to your death.
As above, and you did not have levitation or flying.
You float gently down to earth.
You teleported out of the dungeon but had levitation. You then escape the dungeon.
You fly down to the ground.
You teleported out of the dungeon but had flying. You then escape the dungeon.
You arrive in heaven.  "Thou art early, but we'll admit thee."
You performed a controlled levelport to level −10 or higher.
You find yourself back on the surface.
You performed a controlled levelport to a negative level and were life-saved. You then escape the dungeon.
See also
The Eye of the Aethiopica allows a related technique known as branchporting.
References

↑ random_teleport_level in teleport.c

↑ Barring some corner cases where you hit the edges of the dungeon branch or you would go into the Sanctum before the Invocation. Read the source for those.

↑ teleport.c in NetHack 3.4.3, line 1140

↑ mkmaze.c in NetHack 3.4.3, line 231

↑ src/dungeon.c in NetHack 3.6.6, line 1324