The Ancient Stone Circle is a dangerous location in the western area of the map. The requirements to enter the Stone Circle are non-trivial, which means that generally it is only attempted by quite experienced PCs: in practice, there is no reason to enter the Stone Circle unless an Ultra ending or the Ordinary chaos god ending is being attempted.
In order to access the Stone Circle, the player must meet several requirements: first and simplest, a climbing set is required to access the northwestern region. Secondly, the player must satisfy the Demented Ratling by feeding him six artifacts. The Demented Ratling will then reveal that the Stone Circle can only be accessed during Darknight.
Darknight occurs every 30th day (press Ctrl-E). This means that the player only has two opportunities to visit the Stone Circle before day 90 is reached. On the appropriate day, the player must wait until just before midnight (from 23:00 to 0:00) and press '>' to enter the Circle. In practice, it is possible to repeatedly hit '>' until the Circle is entered, but the timestep for doing so is sufficiently large that there is a small risk that the player may miss the desired time.
|W||Keriax||Multi headed chaos dragon, who holds the Crown of Chaos.|
|h||Chaos Knight||Minion monster.|
|j||Writhing Mass of Primal Chaos||Minion monster.|
|0||Corrupting Pool||Corrupts in addition to usual pool effects.|
Once within, the player will be in a wilderness area with the Temple itself in the centre of the map. Access to the temple is on the left side, guarded by two Chaos knights, two Annihilators. Inside the main room are several Writhing masses of primal chaos, Keriax, the multi-headed chaos dragon, and a pool. The pool is unique in that, in addition to providing the usual pool effects, it also corrupts the PC quite substantially.
The objective in the Stone Circle is to kill Keriax and retrieve the Crown of Chaos that he carries. Keriax is one of the most difficult opponents in the game, with a dangerous corrupting melee attack, a powerful confusion spell that can confuse even players with high willpower and resistance, and deadly chaos breath that can do massive damage and corrupt the player immensely. He also regenerates his wounds. Standing in a direct line with him is strongly not recommended, but may be necessary to hit him with spells of your own or a wand of paralyzation, and it is strongly advised that some sort of disruption effect, such as confusion or blindness, be applied to him, as this makes standing in a direct line safe. Note that chaos breath attack bounces of the walls, so extra attention should be paid to avoid being hit multiple times per one attack. To counteract the regeneration, try to hit him with as many poison effects as possible, and a potion of sickness or even a potion of cure corruption for good measure. If you do need to risk getting hit with a bolt, be at least double resistant, if not immune, to fire, acid, lightning, and ice.
Note that the temple inside has dungeon floor so it is possible to use webs there, whereas they do not work outside of the temple.