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. There is a 20% chance you will stay in place; otherwise, all other eligible levels are equally likely.  This is helpful when you need to travel up.
Level teleport for monsters works the same way and is always uncontrolled. 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 lead to death, and escaping the dungeon if you have an amulet of life saving (or some form of levitation/flying if -1 to -9) if -1 or lower, so they're only good for a few YAFMs.
Restrictions on level teleporting
- 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 up out of your current dungeon branch, but not down.
- The player cannot levelport in Sokoban.
- You cannot level teleport 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 Amulet of Yendor (though you may still quaff cursed potions of gain level).
- You cannot levelport in the Endgame, except in Wizard mode. Even in Wizard mode, you can only levelport to the next or further Planes.
- Controlled levelporting to a negative level will irretrievably end the game: If you have none of levitation, flight, or life saving, you die, while if you have one of those properties, you merely escape. The game will not ask for confirmation before you do this.
- Controlled levelporting to level 0 will normally kill you, but an amulet of life saving will save your life and your game. Note that the game will ask for confirmation before you do this.
- However, that in Wizard mode, with the Amulet, levelporting to -1 through -5 takes you to the appropriate Plane, while without the Amulet but with flight (e.g. polymorphed into a winged gargoyle; levitation is not enough), levelporting to any negative level deposits you on the Plane of Earth with the Amulet.
- You cannot enter the Wizard's tower area in Gehennom 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.
- 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. Additionally, you cannot land on a trap, nor on the vibrating square's location.
Gaining a dungeon level from a cursed potion of gain level has similar restrictions. However, the Amulet of Yendor does not block it, you cannot leave a dungeon branch or the Wizard's tower this way, and you don't run the risk of escaping the dungeon if your Amulet of Yendor was a fake. If you do have the real Amulet and quaff the potion on dungeon level 1, you will immediately enter the Plane of Earth.
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.
- 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
- mklev.c in NetHack 3.4.3, line 1170
- Can_rise_up in Dungeon.c