The Kaernk is a water-dwelling, otherworldly creature that is invisible to the naked eye. Fortunately, it can be detected by the splashes it makes in the water as it "walks" in a slow, deliberate gait.
Originating from the same world as Alexander of Brennenburg, this aquatic nightmare was delivered to the Baron from Johann Weyer as its saliva contained Tampter, an ingredient for a tonic to release Agrippa without killing him. Several water monsters were safely contained within wells in the depths of Brennenburg Castle. However as the events of the Dark Descent unfold, the Shadow following Daniel consumes room after room, until it causes structural failures that allow the deadly Kaernk to escape.
The Kaernk is only capable of attacking things that wander into the shallow pools that it inhabits. However, what it lacks in reach it makes up for with its invisibility. Daniel can only see where the monster is by the loud splashing noises, the water particle effect it makes when moving, and the banging it makes on doors when trying to break them down. It can be assumed that the creature is blind, as it will move toward any disturbance in the water, allowing Daniel to create distance between himself and the Kaernk by throwing objects such as books. However, if any meat is thrown into the water, such as severed body parts, the monster will behave differently; it will pursue and devour the meat, buying Daniel a short amount of time to move in the water unmolested. If Daniel does not disturb the water after throwing an edible object, the Kaernk will return to where it was after it has finished eating, whereas if a book is thrown the creature will remain where it landed. Note also that the Kaernk always "walks", which means that it can be fairly easy to outrun.
The Kaernk is encountered a total of six times, four of which are purely visual encounters with no actual threat. Daniel can catch a glimpse of the creature early in the game as it splashes about below the grating on the floor of the chemical laboratory. The second and most dangerous encounter occurs in the flooded Archives, where Daniel must evade two of the creatures in two areas in immediate succession.
Upon leaving the Flooded Archives, you encounter another Kaernk in a chase to exit the area. This Kaernk is larger but slower than the first; hiding on boxes will do you no good, as it can easily reach and kill Daniel instantly. Daniel must either run all the time and quickly open the doors or slow it down by closing doors behind him in order to escape it alive.
Much later in the game, it can be encountered for a fourth time, in the Cistern. If Daniel's sanity is high enough, he will only hear the Kaernk growl and occasionally splash in the water as he turns the valves, but the creature will not actually pursue or attack him, making it seem like a hallucination. However, if Daniel's sanity has fallen low enough, such as if he has completed the Morgue first, the Kaernk will appear in the water once the last valve is turned, along with the Shadow's fleshy residue. It is a far less dangerous encounter here though, as Daniel can use the many walkways to easily avoid contact with the creature.
As Daniel explores the Sewer, he'll come across a passageway that the Shadow has collapsed completely. Once there, he'll hear the watery predator growl. It seems that the Kaernk is trapped in the rubble from this recent cave-in as it is unable to enter the area and attack him. In low sanity, Daniel may "see" a Kaernk following him.
The final two encounters occur during the quest to recreate Agrippa's Potion, during which you will encounter a well-dwelling Kaernk. To obtain a sample of Tampter, Daniel lowers a haunch of meat into the well and allows the Kaernk to feast on it. If Daniel does not do this at the first well, he will have to do so at the second well located near the Cells. Falling into a Kaernk-containing well is fatal, similar to falling off a ledge in the Choir.
- The word Kaernk is an anagram of "Kraken", the name of a giant octopus in Norse Mythology. It may or may not be intentional. It might also be a reference to Frictional Games being located in Sweden.
- If Daniel stands too close to the edge of a partially-submerged box he's on top of, the monster may succesfully bite and injure him.
- Even though it is invisible, looking at a Kaernk will drain sanity.
- A developer commentary within the Cellar Archives reveals that the Kaernk is nicknamed "Lurky" among Frictional Games employees.
- The in-game model of the Kaernk is a sphere.
- If standing on a small box in the second part of the cellar archives the Kaernk may push away the box and make Daniel fall into the water.
- Judging by the ripples in the water when it moves, the Kaernk most likely walks on at least two hind legs or two large fins.
- It usually cannot reach Daniel if he's standing on a box, even if only a few inches above the water level.
- The Kaernk in the Archive Tunnels is weaker and slower than the ones in the Cellar Archives, indicating greater size to go with its greater power.
- The Kaernk's hissing and defined roars are similar to those of an alligator or a snake.
- It is the only monster/creature in the game that can be killed.