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For the option, see option#boulder.
` Boulder.png
Name boulder
Appearance boulder
Base price 0 zm
Weight 6000

A boulder is a huge stone, represented by ` by default (customisable through the boulder option). Although technically considered items, they behave differently from other items in many ways. If you move onto a square containing a boulder, you will try to push it to the next square in line. If this fails, you will be unable to enter the square, unless your inventory is almost empty (except for gold). Pushing boulders exercises the player's strength, and can be used as a "gym" to make a weak character stronger.

Non-phasing monsters cannot enter a square containing a boulder, except for giants. Giants may stand over and pick up boulders and throw them. A boulder thrown at you ends up on your square, and you may move off it as normal, but cannot re-enter the square without pushing the boulder out of the way. If polymorphed into a giant, you can do the same. Boulders in your inventory while you are a giant have no weight, and you can pick one up even if carrying 52 or more other objects, like a loadstone (it will then be assigned the # inventory slot).

Boulders block line of sight. Monsters cannot attack through boulders, but you can use missile weapons, wands, and spells to attack through them. Wands of striking or spells of force bolt will shatter boulders, but other wands and spells (specifically the wand of digging) will pass over them with no effect on the boulder. Monsters will usually not zap a wand of striking at boulders intentionally, but they may do so as a side effect of targeting you.

Boulders can be used to block corridors, doorways and pits. Boulders are especially useful for crossing water: push them into water and they will create new dry land for you to walk (9/10 chance). If the boulder sinks without a trace, just try again with another boulder.

Boulders are sometimes found as traps, where there is a hidden switch that triggers a rolling boulder, that may crush the player. They can also be summoned by using a scroll of earth. To get past a boulder, the player may break it into rocks with a pickaxe, wand of striking or force bolt. This will transform it into 6 + d60 rocks. It is also possible to take off all armor, drop enough (most) items from the inventory, and squeeze past it. In precise terms, if your inventory is completely empty or you are 850 or more units below your carrying capacity,[1] you can squeeze yourself onto the same square as the boulder.

A spell of stone to flesh turns a boulder into a huge chunk of meat, which is a normal item with none of the boulder's unique properties.

Many players choose to change the symbol for boulders to make them more noticeable, particularly during Sokoban. 0 (zero) is a popular choice.

Boulders are often used to protect stashes or polytraps by pushing one on top of the stash or even many boulders around it as a fort.

Boulders have a 3% chance of falling down stairs if another thrown object lands on their square (even gold). Rocks and gems do not work.[2] You can also push them onto a teleport trap or level teleporter, but you can't control the destination. Similarly, you can knock a boulder down a hole, see the "Boulders on top of pits and holes" section below.

Tactics for pushing boulders

Four of the boulders in this screenshot were blocking the long corridor, but through deft squeezing and pushing the hero pushed them into rooms. If that boulder in the lower-right had started at that position, it would likely be part of a boulder trap.

If you push a boulder, then it will move to the opposite square. In the diagrams below, the # represents where the boulder will move. Boulders on each floor of Sokoban cannot be moved diagonally while solving that level; as of 3.6.1, they can be moved normally once the level is solved.

@     @     @       #     #     #     
 `    `    `   #`@   `    `    `   @`#
  #   #   #           @   @   @       

If there is no space or if it is occupied by a monster (whether hostile, peaceful, or your pet) then you cannot move the boulder in that direction. Failing to push a boulder will not consume a turn. If your inventory is mostly empty, you can squeeze onto the square containing the boulder. (The fastest way to drop your inventory is to press D and then choose option "A" to drop all items.) Such squeezing is useful if there is a door, hidden space, or boulder on the other side.

If a monster blocks the other side and will not move away, you have the option of squeezing onto the boulder and fighting it bare-handed and naked, or you can throw ammunition or Mjollnir or zap wands past the boulder. Be careful when doing so if you cannot see your pets, as they may be the monster blocking you or directly behind it. The player below might want to toss darts, rocks, or other objects at whatever is blocking the way to some holes ^ in Sokoban.


You can move diagonally around boulders (but not in Sokoban) regardless of how much you are carrying. So the following boulder does not block your path provided that you know how to use [yubn] or numpad to move diagonally:


If a boulder is blocking a corridor, and if you are able to push it into a room or into a position like the above, then you can walk around it.

When faced with two consecutive boulders in a corridor, as shown below, you can squeeze past one to push the other.


However, wandering around naked with no wielded weapon, or allowing hostile monster to take from your inventory, might put you in too much danger. You might want to push the other boulder and retrieve your inventory quickly. (The fastest way to retrieve the inventory is to press @ to toggle autopickup on and then move onto the square where you dropped it. Then you might want to press @ again to toggle autopickup off.)

Boulders, like anything else, cannot pass diagonally through open doors. If you need to do that, destroy the door by closing it with c and then kicking it down with Control-D.

The two boulders below are stuck against a wall, and you may only push them in two directions:

-----------          ------           
|...`.....|          |....|    -------
|.........|     #####..`...####......|
|.........|     #    ------    |.....|
---.-------   ###              -------

If a boulder becomes stuck in a corner, then you can not move it at all, even if you squeeze onto its square (unless you are able to dig around it). In Sokoban, a 2x2 square of four boulders (or a 2x2 square of both boulders and walls) is almost likewise stuck, but you might be able to squeeze yourself to free the boulders. (Squeezing causes a luck penalty in Sokoban.) Outside of Sokoban you could have freed a boulder by moving it diagonally, but not if you have two boulders stuck against the same wall.

An example of stuck boulders:

----     ----
|`..     .``.
|...     ....

An example of boulders that are stuck only in Sokoban:

......     ...|..
..``..     ---`..
..``..     ..``..
......     ......

Be very careful in Sokoban to not stick boulders in the above manners unless you are able to solve the level with the remaining boulders.

Boulder creation

A user has suggested improving this page or section as follows:

"clarify how fast monsters dig, if tame dwarfs dig, boulder generation probability, and if it matters if the monster digs intrinsically (all hulks, woodchuck, rock mole) or with a tool"

  • Sometimes, a newly created ordinary level will contain randomly placed boulders.
  • Rolling boulder traps always have a matching boulder. If a boulder generates in a room rather than in a corridor, there is a trap nearby. Push the boulder one square in any direction to disarm the trap.
  • Sokoban levels have boulders in fixed places. See Sokoban for special properties.
  • Giants and titans will often have a boulder in their starting inventory (except if reverse genocided).
  • Digging monsters will leave a boulder on 8.3% of all tiles of diggable rock they burrow through.[3]
  • Reading a scroll of earth while not confused, with results depending on the scroll's BUC status.
  • Polymorphing statues will sometimes produce boulders.
  • You can wish for one boulder at a time.

In the endgame, except for the Plane of Earth, only polymorphing statues, randomly spawned giants, and wishing are sources of boulders.

Detailed treatment of boulder, hole, and pit interaction

A user has suggested improving this page or section as follows:

"There may be some research to be done pertaining to trapdoors."

Boulders can be used to fill holes and pits, but the exact messages given and effects depend on a couple factors: whether the boulder or the pit/hole occupied the space first; assuming the boulder came second, where did it come from; assuming the pit/hole came second, how was it made; and where you are standing in relation to the pit/hole.

Pushing a boulder into a pit removes the boulder and the pit, and buries any items in the pit (including other boulders if they happen to be in there, strangely enough, though getting boulders into a pit without filling it is a challenge, see the section below). Pushing a boulder into a hole removes the boulder and the hole and destroys any items in the pit, including other boulders sitting on top of the hole (again, see the section below).

If a boulder is pushed into a hole the hole will be plugged, producing the message "The boulder falls into and plugs a hole."

If a boulder is dropped by a levitating giant, thrown by a giant, wished for by a levitating player who is not a giant and therefore cannot hold the boulder ("Oops! The boulder drops to the floor!"), dropped from the sky via a scroll of earth while the player stands next to the pit or levitates over it, or rolled by a rolling boulder trap into a hole, the hole will be plugged and the message "The boulder plugs a hole." produced.

If any of these methods (pushing, dropping as a levitating giant, throwing as a giant, dropping as a levitating non giant via wishing, reading a scroll of earth while to the side or levitating, or activating a rolling boulder trap) is used to fill a pit, the message will be either "The boulder fills a pit." or "The boulder triggers and fills a pit." depending on whether or not the pit was known.

The situation is slightly more complex if you are in the pit when a boulder is dropped into it. (This can happen if while in the pit and not levitating you use a cursed or uncursed scroll of earth, drop a boulder as a giant, throw a boulder up or down as a giant, wish for a boulder as a non giant, or have a monster trigger a rolling boulder trap that sends a boulder down on top of you. Presumably it can also happen if a giant can be convinced to throw a boulder at you while you're in the pit.)

If a boulder is dropped/rolled into a pit while you're in it, the "The boulder drops into the pit with you.". If you are a giant, the pit is filled and you are instantly freed from the pit (so a cursed scroll of earth would be a fast way for a giant to escape a pit trap). If you are not a giant, the pit is not filled until you escape from it. Escaping will take longer than normal because there is a chance each action that your leg gets stuck. ("Your leg gets stuck in a crevice." immediately followed by "You free your leg.") If you zap down (not up!) or apply a wand of teleportation before escaping, the boulder will be teleported away; this will allow you to escape the pit like normal, the pit will not be filled, and the boulder will not be removed.

You cannot be "in" a hole, so filling a hole while standing on it is the same as filling it while standing near it.

More interesting still are situations in which the pit/hole is created underneath a preexisting boulder. (This is easy in wizard mode, just wish for a pit or hole while standing on a boulder.)

One way to dig under a boulder is to move into it as a giant or squeeze into its space as a non giant. This requires that the boulder cannot be pushed in the direction you're moving from. Once on it, you may zap a wand of digging downwards. This will produce either a pit or a hole, depending on whether the level you are on has diggable floors. The pit or hole will be filled immediately with the message "KADOOM! The boulder falls in!" and nothing will be able to fall through the hole before it is closed.[4]

Attempting to dig down with a pick-axe while on a boulder will fail, "There isn't enough room to dig in here."

It is possible to create a pit under a boulder by applying a charged drum of earthquake. If you are within sight of the boulder this will produce the message "KADOOM! The boulder falls into a chasm!". If you are standing on the boulder when you apply the drum of earthquake you will instead see "KADOOM! The boulder falls into a chasm below you!".[5] Either way, the boulder will immediately fill the pit. Interestingly, unlike digging a pit under a boulder with a wand of digging, this will immediately bury every item on the square with the boulder. (If there are multiple boulders on the square where the pit is created, all but one will be buried, and the extra one will be removed (it "filled the pit").)

It is not possible to create a pit or hole underneath a boulder by breaking a wand of digging, there are special checks in place to prevent this.[6][7][8]

There is one more message than can be produced by filling a pit with a boulder. First, obtain a pit with a boulder sitting on/in it (no distinction is made between being "on" or "in" for items, including boulders) on a diggable floor (see the next section), then stand on the boulder and zap digging down. There is a 50% chance of getting the message "The boulder settles into the pit.", otherwise you will get the standard "KADOOM! The boulder falls in!".[9]

While you can get a boulder over a hole, you cannot get on top of it to zap digging downwards, because you must be levitating to float over the hole, and when levitating you cannot move on top of or squeeze in with boulders (the levitation check takes place before the "are you trying to push the boulder or get on it" check). You can, with luck, get on top of a hole without falling in, but this seems to be impossible when there is a boulder on the square.

Boulders on top of pits and holes

Normally, any action that would put a boulder on top of a pit or hole would fill the pit or plug the hole. The easy way around this is to be in wizard mode and wish for a hole or pit while already standing on a boulder. However, it is possible, albeit probably a waste of time, to do this in a non wizard game as well.

First, obtain a pit or hole of your choosing. Drop a (preferably blessed) statue on top of it, either by levitating or stepping on top of it (with a hole you can get lucky and not fall in). Now polymorph the statue until it becomes a boulder. If your boulder is over a pit, you can step onto it and achieve the "The boulder settles into the pit." message mentioned above. If your boulder is over a hole you can throw items at it, like gold, and the boulder will eventually fall down the hole, without plugging it, and land on a lower level.

Pushing multiple boulders

When there is more than one boulder on a square, when you move to it, you will try to push each boulder in turn until one of them does not move.

Encyclopedia entry

I worked the lever well under, and stretched my back; the end
of the stone rose up, and I kicked the fulcrum under. Then,
when I was going to bear down, I remembered there was
something to get out from below; when I let go of the lever,
the stone would fall again. I sat down to think, on the root
of the oak tree; and, seeing it stand about the ground, I saw
my way. It was lucky I had brought a longer lever. It would
just reach to wedge under the oak root.
Bearing it down so far would have been easy for a heavy man,
but was a hard fight for me. But this time I meant to do it
if it killed me, because I knew it could be done. Twice I
got it nearly there, and twice the weight bore it up again;
but when I flung myself on it the third time, I heard in my
ears the sea-sound of Poseidon. Then I knew this time I
would do it; and so I did.

[ The King Must Die, by Mary Renault ]


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