Castle Karstaag Caverns The Castle Karstaag Caverns consist of a small , multilevel cave in . They are located in the northwestern section of the island of Solstheim , east of Northshore Landing and west southwest of Glacial Cave . Sublocations . Castle Karstaag Courtyard . This is reached at the end of the caverns . There is an exit here to Solstheim , as well as Karstaag ' s throne . It is also known as the Castle Karstaag Ruins . Walkthrough . At first , this is the only way to enter the Castle Karstaag Ruins , since the door to the Ruins are locked beforehand and the Dragonborn only is able to acquire a key to the door after defeating and looting a Bristleback inside . The cave starts heading west next to a stream , then turns left ( south ) where it opens to a large body of water filled with ice that must be swum across . Against the left ( south ) wall is a small ice shelf with the corpse of Esmond Tyne . It has some random loot , as well as the Bonemold Formula , which can be returned to Glover Mallory to complete the miscellaneous quest " Paid in Full . " There are several rieklings in the area shooting their spears from above . On the right side is a large ice shelf that can be climbed onto . At the southern end of the room , in front of a waterfall , is a bridge . Across the bridge to the left ( south ) is a riekling camp containing a knapsack with leveled loot , plus a riekling hut . Under the water beneath the waterfall is a locked chest . Back across the bridge , another cave leads west , where more rieklings are found . The cave narrows , then turns right ( north ) . It opens to a small room with several more rieklings around a campfire and a raised , fenced area that cannot be reached yet . Turning left ( west ) , another cave leads to an ice - covered door . Beyond the door , the cave drops down to where the floor is covered with water . then turns north . There is an novice - locked ice - covered door along the right ( east ) wall with minor loot behind it . The cave then comes to a T intersection . To the left ( west ) are two doors - a novice - locked door to the right ( north ) with nothing behind it but a soul gem , and an apprentice - locked door to the left with nothing behind it but a riekling corpse . Back at the T intersection , to the right ( east ) , a short path leads to a door . Behind the door , the cave leads up out of the water , then turns right to the raised platform seen earlier . On the left ( east ) end of this platform , a short passage leads back to a riekling camp that overlooks the first large room in the cavern , with a bridge that spans this level . Before crossing the bridge , a very narrow ledge against the right wall leads to a few soul gems and a riekling hut with random loot . Across the bridge to the east is another riekling camp with several more rieklings . Beyond that , a cave leads up to another large room with boxes to the right that have an apothecary ' s satchel lying on top . To the left ( north ) is a ramp down to the ground floor of the room , where three bristleback s and a riekling are found next to another waterfall . In a crevice to the southwest is a novice - locked chest with a Dibella statue . Back up at the entrance to the room , the path continues south , turns right ( west ) , and leads to a door that opens onto an even higher overlook of the first large room in the cavern . Another small riekling camp here has two rieklings protecting it . A bridge leads west across this highest level of the room . At the other end of the bridge , another bridge to the left ( southwest ) leads to another camp with more rieklings , another riekling hut , and a chest next to the water containing leveled loot . A path leads west , then turns right ( north ) and leads to the Castle Karstaag Courtyard ( which is synonymous with Castle Karstaag Ruins ) . Castle Karstaag Ruins . Upon arriving here , there is at least one mounted riekling , as well as several others who are not . The mounted riekling has the Castle Karstaag Key on its corpse . In addition , there is Karstaag ' s throne , which can be activated if Karstaag ' s skull is in inventory ( obtained from Glacial Cave ) . See the Karstaag article for details . A master - locked door to Solstheim can be opened with the key . Quests . Paid in Full . Glover Mallory ' s formula for creating bonemold armor was taken by Esmond Tyne , and he wants it back .