Clairvoyance
Clairvoyance allows you to intermittently map an area of the dungeon around you, showing elements such as corridor walls and stairs.
Contents
Effects
When the effects of clairvoyance occur, a 19×11 region around you is mapped and revealed. Like magic mapping, the map will remain unlit and will not reveal secret doors or traps. As of NetHack 3.6.2, clairvoyance will also reveal objects (but not their appearances) and mark unseen monsters as I in the affected area. Also, having intrinsic or extrinsic clairvoyance allows you to cast the spell of clairvoyance as if you were Skilled in divination spells.
If you have clairvoyance as an intrinsic or extrinsic, the effect of mapping the area around you is not constant, but will occur with 50% probability every 15th turn, unless you are in the endgame.[1]
Having intrinsic clairvoyance exercises wisdom every 5 turns, unless it is blocked (by wearing a cornuthaum as a non-wizard).[2]
The following information pertains to an upcoming version (NetHack 3.7.0). If this version is now released, please verify that the information below is still accurate, then update the page to incorporate it.
The clairvoyance property does not have a 50% chance of activating every 15th turn, but instead activates every 15–45 (average 30) turns after the last activation. Relevant commitGaining clairvoyance
Intrinsic
You can only ever get intrinsic clairvoyance temporarily, for a random length of between 500 and 999 turns, by donating between xplevel*200 and xplevel*400 to an aligned priest if this is more than one-third of your visible gold.[3] Repeated donations for clairvoyance stack, and can be useful for speed running. By losing levels to level 1 (see drain for gain), a character can cheaply get clairvoyance by dropping or stashing all their gold, taking 200 (or 400, but not 600) gold at a time into main inventory, and donating it 200 at a time. For 1000 gold, you can get between 2500 and 5000 (averaging about 3750) turns of clairvoyance, which may last for the rest of the game and will make exploring Gehennom much faster.
Extrinsic
Clairvoyance can only be obtained as an extrinsic by wearing a cornuthaum as a wizard, or by carrying the Amulet of Yendor.
Single-use
You can get a single application of clairvoyance by casting the spell of clairvoyance, which is a level 3 divination spell. It has slightly different effects when cast at Skilled or above; see the spell's page for details.
Strategy
Clairvoyance is similar to a limited form of magic mapping; however, clairvoyance will reveal the map surrounding you on levels that cannot be mapped by magic mapping, such as the Valley of the Dead. A common strategy is to obtain intrinsic clairvoyance from an aligned priest just prior to entering the Valley and Gehennom beneath it. Alternatively, you can save up money while in the Dungeons of Doom and donate it all for clairvoyance to the priest of Moloch in near the end of the Valley of the Dead; it is often possible to perform around 8-9 donations for clairvoyance, which will last long enough to help you map a significant proportion of Gehennom.
Variants
DynaHack, FIQHack and GruntHack
DynaHack, FIQHack and GruntHack have the clairvoyance object property that is applicable to armor.
SLASH'EM
Besides these sources of clairvoyance, there is also the potion of clairvoyance. A blessed potion will give you intrinsic clairvoyance for between 100 and 149 turns; an uncursed potion gives you a single application of clairvoyance.
