The Crypt of Kryl'Feijan – or the "Dark Crypt" as it is known in game – is a zone that can only be accessed through a random event, in a manner similar to the Unknown Tunnels. The player may trigger this event while traveling on the world map over the western Maj'Eyal continent after reaching level 25. The option to enter this zone will only be presented once to the player.
The Dark Crypt has 5 floors. The top 4 floors are relatively small in size, and consist of a dungeon layout with narrow corridors connecting larger rooms. Most of the area is unlit. These levels are very dangerous due to the cramped quarters and high density of enemies. Many people skip this zone when it is offered because of its deadliness. If you wish to tackle this zone, it is recommended that you stockpile some blight resistance items and bring them with you when you are nearing level 25+.
The opposition consists mainly of various Rhaloren units that can use Shalore racial talents: blood mages, tempests, cultists, and guards. There may also be some minor demons and Ogres. The elven cultists are particularly dangerous, since they can use to teleport you around, and potentially cause you to aggro more enemies than you can handle. Magical diseases that debuff your strength can also cause you to exceed your encumbrance limit, and prevent you from moving when you are most vulnerable.
Taking the stairs to the bottom floor, you will enter a large hallway that is sealed with a locked door, and you will receive the quest The Sect of Kryl-Feijan. A group of 4 Acolytes of the Sect of Kryl-Feijan are preparing a summoning ritual around an altar. There will be a 20-turn time limit displayed on screen. Each Acolyte killed will extend this time limit by 6 turns. The locked door will open when all 4 Acolytes are dead, or when Kryl-Feijan is summoned (see below).
Should you fail to kill all the Acolytes before the timer expires, the sacrificial maiden on the altar will be consumed, and the powerful demon Kryl-Feijan will spawn to fight you. If you manage to stop the ritual in time however, then you will free the human woman named Melinda, and you must then escort her out of the crypt by keeping her safe until you find the stairs. In order to escape together with Melinda and complete the quest, she must be adjacent to you when you take the exit stairs. While she's alive, you can't leave without her.
An easy way to keep Melinda safe is to dig a winding path into the thick walls next to the altar room. One can lead Melinda into this path, then park her there, either by moving away quickly or using some method of teleportation. After the path ahead has been cleared of all threats, she can then be safely escorted to the exit. Alternatively, due to the relatively low density of enemies on this floor, one can also just dig a path along the map edges towards the exit stairs and avoid most enemies this way.
After escorting Melinda out of the dungeon you will be able to find her in Last Hope by visiting the rich merchant's house (in the far south). Her father will give you a reward (randomly chosen artifact), and you can start a romance sub-plot.