# Altar

Dungeon features

&nbsp;&nbsp;Air

_&nbsp;Altar

#&nbsp;Corridor

#&nbsp;Cloud

#.&nbsp;Drawbridge

+-|&nbsp;Door

.&nbsp;Doorway

{&nbsp;Fountain

|&nbsp;Headstone

.&nbsp;&nbsp;Floor

&gt;&lt;&nbsp;Ladder

.&nbsp;Ice

#&nbsp;Iron&nbsp;bars

}&nbsp;Lava

}&nbsp;Moat

#&nbsp;Sink

&nbsp;&nbsp;Solid&nbsp;rock

&gt;&lt;&nbsp;Staircase

\&nbsp;Throne

^"&nbsp;Trap

#&nbsp;Tree

-&nbsp;|&nbsp;Wall

~&nbsp;Vibrating square

Wikipedia has an article about:
Altar

Religion in NetHack

priests
alignment
alignment record
altars
atheism
anger
gods
sacrifice
prayer
turn undead

An altar, represented by an underscore (_), is a place where you may worship gods. Temples contain an altar and an aligned priest.
Altars are co-aligned if they are of the same alignment as you and cross-aligned if they are of a different alignment. To determine if an altar is co-aligned, either use far look or stand on it and use close look. Altars of Moloch are unaligned. Unaligned altars appear only in Gehennom, one variant of Minetown and some quests (except as mimics).
Altars are scattered randomly throughout the dungeons. Minetown has a randomly aligned altar and unaligned altars can be found in the Valley of the Dead (in the temple of Moloch), Orcus-town and Moloch's Sanctum unless they were destroyed in a bones file. The variant of Minetown that has been overrun by orcs has an unaligned altar.
Altars can be used to detect the BUC status of items. This is done by dropping the item onto the altar. A black flash marks a cursed item and an amber flash a blessed one. You cannot detect the BUC status if you are blind. You cannot detect whether an item is blessed or cursed if you are hallucinating, as you will not be able to distinguish between amber flashes and black flashes; you can, however, identify uncursed items, as there will not be a flash at all.[1]
If you #sit on,[2] engrave on,[3] or kick[4] an altar, you will experience negative effects depending on the altar alignment and your alignment record. If the altar is co-aligned and your alignment record is greater than -rn2(4), you lose one point of wisdom and one point of alignment record; otherwise, you lose 0-2 points of Luck, if your Luck is greater than -5.[5] This can be used to deliberately lower your Luck or alignment record to prevent crowning. This does not break atheist conduct.
If you (or a monster) zap a wand of digging downwards, you get the message "The digging ray is ineffective" and nothing further happens. However, if you break a wand of digging or apply a drum of earthquake while standing on an altar, it will be destroyed (unless it is a high altar).
Standing on any altar scares vampires as if you were standing on Elbereth or a scroll of scare monster.[6]
Randomly generated altars appear in ordinary room and corridor levels in the Dungeons of Doom. There is an independent 1 in 60 chance of each non-special room containing an altar,[7] which gives a 93% chance of at least one. The altar has an equal probability of each of the three alignments. Altars will not be generated adjacent to doors (diagonal is okay), but otherwise can occupy any spot in the room not already occupied by something else.[8] The chance of an empty room containing an altar does not change with dungeon level.

Contents

1 Sacrificing corpses
2 Making holy/unholy water
3 Altar camping
4 High altars
5 Hallucinating colors
6 Encyclopedia entry
7 Variants
8 See also
9 References

Sacrificing corpses
Main article: Sacrifice
Sacrificing fresh corpses is a useful way to reduce your prayer timeout, increase your luck, gain powerful artifact weapons, and improve your alignment (particularly if your god is unhappy with you). In SLASH'EM, you can also have wielded and worn items blessed and gain powerful minions through sacrifice. Sacrificing at the altar of another god has a chance of converting that altar to your alignment, potentially angering that god. Note that it also has a chance of converting you to that altar's alignment, angering your god and making it difficult or impossible to complete the quest if you haven't already done so.

Making holy/unholy water
If you drop one or more potions of water onto an altar and #pray, the potions become blessed if the altar was aligned with you and become cursed if the altar was not aligned with you. This occurs regardless of whether the water was blessed or cursed before. Be aware that water praying on a cross-aligned altar will anger your god, decrease your luck, and possibly cause you to be punished in some other way.
Normal prayer timeouts apply when praying on altars.

Altar camping
It is generally possible to survive indefinitely on a level with an altar. Under normal circumstances, the need for food drives you to deeper unexplored levels. However, you can instead pray when weak, and sacrifice to reduce your prayer timeout back to zero. Doing this for extended periods of time can net you many death drops, as well as a collection of gifts from your god if your luck is substantially high. This is considered by some to be degenerate.
In older versions, this was most effectively done with black puddings or brown puddings, which was known as "pudding farming"; brown puddings were less suitable for farming due to a lower sacrifice value, the inability to be summoned by kicking a sink, and their tendency to not leave a corpse (meaning more work and fewer death drops), but this was offset by their lack of a damaging attack, allowing them to be farmed more safely by physically weak or low level characters. As of Nethack 3.6.0, however, puddings no longer leave corpses at all, rendering this strategy totally ineffective.

High altars
The three altars on the Astral Plane and the altar in Moloch's Sanctum are considered to be high altars. They act largely as normal altars, but cannot be converted under any circumstances; doing so will cause the god in question to attempt to zap you and, failing this, will summon three minions to protect the altar. In addition, it is not possible to sacrifice monsters unless you are holding them (to prevent sacrificing the Riders).
To correctly ascend, one must #offer the real Amulet of Yendor (held in main inventory, not dropped on the altar) at the altar of your alignment. Determining the alignment of the altar requires standing on its location and using the : (look) command. The ; (farlook) command does not give information about a high altar's alignment (it merely calls it "aligned," which does not mean "coaligned with you," as a number of new players learn the hard way). Other methods to detect the correct altar are to zap a probing at the high priest, or to note if you are given sanctuary (that is, all monsters other than the Riders, aligned priest, and angelic beings, will not be allowed to enter and cannot attack you with melee attacks). If the version of NetHack you are playing on has not fixed the Astral call bug, that is also a possibility.
You can destroy the chaotic altar with non-chaotic same-race sacrifice, but you cannot convert the others.

Hallucinating colors
If you drop a blessed or cursed item on an altar while hallucinating you will see a 

<color> flash, where <color> is randomly selected from: "ultraviolet", "infrared", "bluish-orange", "reddish-green", "dark white", "light black", "sky blue-pink", "salty", "sweet", "sour", "bitter", "striped", "spiral", "swirly", "plaid", "checkered", "argyle", "paisley", "blotchy", "guernsey-spotted", "polka-dotted", "square", "round", "triangular", "cabernet", "sangria", "fuchsia", "wisteria", "lemon-lime", "strawberry-banana", "peppermint", "romantic", "incandescent".[1][9]

Encyclopedia entry

Altars are of three types:
1.  In Temples.  These are for Sacrifices [...].  The stone top will have grooves for blood, and the whole will be covered with _dry brown stains of a troubling kind_ from former Sacrifices.

[ The Tough Guide to Fantasyland, by Diana Wynne Jones ]

To every man upon this earth
Death cometh soon or late;
And how can man die better
Than facing fearful odds
For the ashes of his fathers
And the temples of his gods?

[ Lays of Ancient Rome, by Thomas B. Macaulay ] 

Variants
Players of NetHack brass and SLASH'EM need to be wary when converting altars, because of the increased chance that the altar's original god will dispatch a minion against you. At experience level 7 or above with high alignment, the chance of a minion appearing after converting the altar is the same as vanilla.[10][11] As in vanilla, the god will yell, "Thou shalt pay for thy indiscretion!"[12] Players with a high luck will have fewer minions dispatched against them.
Even worse, there's an additional chance of one or more minions appearing post-conversion. In SLASH'EM, if you are at experience level 4 or above, there is a chance that "You feel (god) is very angry at you!" and the god dispatches two minions.[13] Afterwards, you still have the original chance of another minion, as above. Again, luck is a factor.
In NetHack brass, you will always receive "You feel (god) is very angry at you!" For all experience levels, at least one minion will appear. Two rolls are made: the first from 0 to 9, the second from 0 to 19.  For each roll, if your level is less than the generated random number, a post-conversion minion is summoned.  Luck is not a factor. Thus in brass it is very dangerous to convert altars. You might convert an altar at experience level one and have to flee to another level from one minion, or three minions if the game rolled 0 twice, thus giving you no use of the converted altar. If converting an altar at experience level 7 or above, you might still get the pre-conversion minion, forcing you to fight as many as four summoned minions.[14]
Also, there seems to be a possibility in SLASH'EM to have equipment being worn blessed if you sacrifice enough.

See also
Prayer is closely related to sacrifice. See that page for altar-related intrinsics, crowning, etc.

References

↑ 1.0 1.1 doaltarobj in do.c

↑ src/sit.c in NetHack 3.6.6, line 137

↑ src/engrave.c in NetHack 3.6.6, line 576

↑ src/dokick.c in NetHack 3.6.6, line 1061

↑ src/pray.c in NetHack 3.6.6, line 2232

↑ monmove.c in NetHack 3.4.3, line 129

↑ mklev.c in NetHack 3.4.3, line 785

↑ mklev.c in NetHack 3.4.3, line 1353

↑ hcolor in do_name.c

↑ pray.c in SLASH'EM 0.0.7E7F2, line 1606

↑ pray.c in NetHack 3.4.3, line 1396

↑ minion.c in NetHack 3.4.3, line 128

↑ pray.c in SLASH'EM 0.0.7E7F2, line 1583

↑ src/pray.c in brass 040923

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