In Caves of Qud, there are a total of 52 achievements awarded for completing certain tasks. Of these 52, 20 are hidden, meaning that neither the requirements for completion nor the achievement's icon are displayed until after the player has completed them. These hidden achievements are displayed further down, in a separate section from the non-hidden achievements.
These are currently only available for players playing on Steam clients.
Through some method, gain a reputation of +700 or more with one of the in-game Factions.
This can generally be achieved most easily by becoming loved by the player's starting village, as the player can water-ritual with the Mayor, the town's Warden, and the town's Questgiver.
From there, one must either kill creatures disliked by the village, perform a Water Ritual with creatures liked by the village, or use Schrodinger pages from the Annals of Qud to increase their reputation further.
Biographer
Learn the complete history of a single sultan.
Learn every piece of historical gossip about the life of a single Sultan.
Gossip can be learned through a combination of viewing statues, gossiping, and looking at painted or engraved items.
Throw an artifact worth 200 reputation or more into the Sacred well.
A timecube or phase cannon is the only artifact valuable enough to gain 200 reputation when cast into the well.
If you have it, it is a good idea to use Precognition (or a Sphinx salt injector(favilink error!), if you are True Kin) before offering to the well so that you can gain the achievement and still keep your artifact.
Eat an Entire Bear
Kill a bear and eat it. Just eat an entire bear.
Kill a bear and eat its corpse raw by picking up the Bear corpse, waiting until you are famished or hungrier, and choosing to eat it.
Players with the Carnivorous mutation need not wait until they are famished.
Friend to Fungi
Host 3 different fungal infections at once.
This can be easily done by walking near three different color broodpuffs. Make sure that one fungal infection already grows before walking into the next one, as itchy skin does not stack and walking into more spores will not change the infection type.
Gemini
Wield Caslainard and Polluxus.
Kill Svenlainard, Trophy Hunter and wield his two swords. He is not affiliated with the Village of Kyakukya, so you do not need to worry about others joining in the fight unless you have area of effect moves.
The lair of Oboroqoru, Ape God is a hidden lair in the jungles around Kyakukya. Apes will also trade you the location if you have reputation with them.
Jawsnapper
Kill 100 snapjaws.
There's so many of the little buggers. Play long enough and you'll get it.
This is a very rare achievement due to based mostly on the random chance that you will come across a legendary frog lair, and have enough reputation for them to teach you Jump. ice frog lairs are generally located in the Jungle biome.
Love at First Sign
Fall in love with a sign.
Mouse control is required for this achievement, as looking through keyboard forces the cursor to center on yourself, making you fall in love with yourself instead. Turn on mouse controls, apply love injector, and right click a sign to look at it.
Love Thyself
Fall in love with yourself.
Inject yourself with a love injector, and look at yourself (press l).
Mutagenic Mastery
Advance a mutation to level 15.
Peekaboo
Become loved by newly sentient beings.
Proteus
Have 10 mutations.
Can be easily done by creating a character that has a 4 point defect and choosing all the cheapest mutations possible.
Phase back into the corporeal realm inside a wall while surrounded by walls.
The Spirit of Vengeance
Recover the Ruin of House Isner.
The Woe of Joppa
Become hated by the villagers of Joppa.
Three-Sludge Monte
Kill a trisludge.
Proselytize or beguile a sludge(favilink error!), and dump 3 different liquids on it. Then wail on the helpless thing. It must be a Trisludge, any more and it will not count.
Five-Sludge Monte
Kill a pentasludge.
Ten-Sludge Monte
Kill a decasludge.
To Thine Own Self Be True
Wear your own severed face on your face.
Through some method, manage to get your face severed off, regenerate it, and then equip your severed face in your face slot.
Note that Ironshank must actually be contracted. Using honey or Yuckwheat stems to stave off the disease after getting the "Your legs ache at the joints" message will not count.
Note that Ironshank must actually be contracted in order to be cured. Staving off the disease using honey or Yuckwheat stems will prevent you from contracting the disease and thus prevent you from curing it.
Note that Glotrot must actually be contracted. Using honey or Yuckwheat stems to stave off the disease after getting the "Your throat feels sore" message will not count.
Cure Glotrot using the method described in the CorpusCholiys.
Note that Glotrot must actually be contracted to be cured. Staving off the disease using honey or Yuckwheat stems will prevent you from contracting the disease and thus prevent you from curing it. This also counts for the Synolimb achievment.
Shoot.
Get killed by a chute crab.
Easily done if entering Golgotha blind. For a dedicated build for this, take precognition and wings, fly to Golgotha, and precog until you find the shaft with "scratched vents" and wait.
timecube, and then activate it. A 
sacred well.
bear and eat its corpse raw by picking up the Bear corpse, waiting until you are famished or hungrier, and choosing to eat it.
Svenlainard, Trophy Hunter and wield his two swords. He is not affiliated with the Village of 
Kyakukya, so you do not need to worry about others joining in the fight unless you have area of effect moves.
Mamon Souldrinker and equip the 
amaranthine prism that he drops.
goat.
Oboroqoru, Ape God is a hidden lair in the jungles around 
Stopsvalinn can be easily gotten from trading secrets from the Barathrumites or Trolls.
ice frog lairs are generally located in the Jungle biome.
love injector, and right click a sign to look at it.
helping hands. Or, dominate an insect that has 6 legs.
Golgotha or the deep shaft in 
Bethesda Susa.
Ruin of House Isner.
Corpus Choliys.
oddly-hued glowpad in the Salt Marsh. They will be located in the center zone of a random Salt Marsh pasarang.
regeneration tank, or applying an 
ubernostrum injector after losing a limb. Regenerating a tongue to cure Glotrot also counts for this achievment.
Q Girl.
