Southfringe Sanctum

 is a cave located in. It is a remote snowy cave that is home to the Spellsword warlord Bashnag and his coven.

Location
From Fort Neugrad, follow the trail that would lead to Falkreath, watching for a trail that forks to the south. Following that southerly trail will eventually lead to a small path down to Southfringe. An Alchemy Lab and a Spellsword will be at its entrance. Use caution when entering, the first gate is protected by a Frost Rune.

Layout
The cave entrance leads to a large main chamber with two parallel paths leading from it. The top path will lead towards Bashnag and his Spellsword coven, while the bottom path will lead towards a Giant Frostbite Spider lair. The main chamber itself is fairly large with trees growing in it. On the top will be a Spellsword working on an Anvil and a unique fox named Pumpkin. Continuing through the top is another Spellsword working on a Alchemy Lab just before Bashnag's room. Bashnag himself is working on an Arcane Enchanter, it is easy to get by without him noticing while he is on the Arcane Enchanter. He carries the Destruction skillbook, The Art of War Magic and an augmented loot chest can be found in the corner of the room.

Enemies
The Frostbite Spider area has lots of small-sized Frostbite Spiders along with one giant spider. Several egg sacs with Spider Eggs can be found throughout this portion. Selveni Nethri will be strung up in webs in a small side passage off this room.

The Savior of Selveni Nethri
Selveni Nethri can be found stuck in webs in an offshoot from the passage either before or after killing Bashnag. Cut her down and speak to her to begin a miscellaneous quest to help her escape the cave. Carefully attack the web to free Selveni without harming her, then speak with Selveni to gain a new Side Quest that involves clearing the cave so that she can safely escape on her own. Tell her to wait until all enemies are dead, then return and announce to her that it is safe to exit.

Quests

 * The Break of Dawn Meridia's Beacon can be located here.
 * Possible location for any of the ancient Dawnguard relics during the quest Lost Relic.

Inside

 * A chest is hidden behind a tree near the entrance.
 * The Art of War Magic can be looted from Bashnag.
 * Ancient Nord cuirass can be looted from Bashnag as well.
 * A boss chest in the room where Bashnag is found.
 * There's an urn on a tree near the cage with a chicken and another leaning on the tree behind it.

Outside

 * Due north of the cave is a chest next to a tree and skeleton, with The Warrior's Charge leaning up against it, a Conjuration Skill Book
 * Silver Ore Vein: Just west of that chest, in a small alcove.
 * Moonstone Ore Vein: Due south of the cave entrance, follow the path to the blocked gate to Cyrodiil. The vein is right by the gate.
 * Just above this Vein (over the rocky area in front), will be a snowy opening. Follow the side of the right rock wall to get to two more Moonstone Ore Veins.

Facilities

 * Alchemy Lab is along the right path and another one at the cave's entrance
 * Arcane Enchanter - In Bashnag's Room
 * An Anvil - In the large chamber

Trivia

 * The items and enemies inside this cave do not respawn.
 * To the south of this location, the Gate to Cyrodiil can be found.
 * There is a Silver Ore Vein after the first gate on the left by the tent and cage.
 * There is a Fox named Pumpkin inside Southfringe Sanctum.

Bugs

 * Lydia and Illia can get stuck on a small landing between two trees just below the cage with a chicken in it. She doesn't seem able to take the small step down to the next level. And that blocks the completion of the The Savior of Selveni Nethri.
 * Solution: Move around her for a bit on the lower section, she will figure it out.
 * Selveni Nethri can get stuck right before the exit/entrance to the cave (she needs to leave the cave to complete the quest). If this happens help her out by using the Unrelenting Force shout to push her outside. If the Dragonborn lacks the shout, a weak ranged destruction spell such as Flames or Frostbite may be used to turn her hostile. When she attacks, lead her around the cave's circuit and back out the exit. (This may take several tries.)
 * Once given the quest and hitting the "show me this location" function the map may indicate an area far removed from the actual location of Southfringe Sanctum.
 * The Dragonborn can jump up and out from the cave in the last "room" by jumping between the rocks.
 * To the left of Bashnag's chest there is an opening in the rocks.  If you can get through there (I used Sneak, but couldn't repeat) you end up "behind" the graphics (under the mountains).  You can wander around on a perfectly flat plain (I don't suggest going off the edge) or re-enter the game by walking back into the mountain.  It's neat.