Bristleback Cave is a dungeon in Skyrim: Dragonborn
Found on the Northwestern coast of Solstheim.
Head to the North down the tunnel in front of you. Going toward the fencing you will find some dead reavers. Approaching the bodies will trigger a Riekling burst out of a nearby barrel.
Turn to the West after that and follow the path around to the South. This will lead to a large room. There are just a few things to be found here. Collect them and then head back to where the Riekling burst out of the barrel.
This time, head to the North. Go down the slope and you will find a number more Rieklings. Take your time to clear out this room. When you have head to the East.
You will come across another split in the path. It will go to the North and South.
Go to the North to find a short corridor leading to another room. This has more Rieklings about in it. There are a number of Huts that you can loot here. Exploring around will yield a number of useful potions in this section. When you reach the far end, more rieklings will appear in the area.
Head to the East to continue farther down this path. There is a pair of Rieklings hiding in the nearby snow pile. Follow this path to the North.
This will lead to another Riekling camp. There are at least 4 Rieklings in this area. Clear it out and then find the path to the South.
This will lead deeper in and to another section of the Riekling camp. there are more Rieklings scattered around the back portion of the camp. Take them out carefully. Go to the back left portion of this camp to find an East Empire Lockbox
Head down the path leading to the West in front of the pile of stuff in front of this part of the Riekling camp. This leads down a slope with another Riekling hidden in the snow. There are more twists that will lead you to more Rieklings that are hidden in barrels. Follow the path around the switchback and down the slope to the West.
Another Riekling camp rests at the bottom of this slope after the switchback. There are just a few Rieklings around the area and a number of Soul Gem Fragments. Defeat the Riekling and head to the West, down the slope there.
Go on down the slope to the West. Another small Riekling camp awaits at the end of this corridor. There is a visible Riekling and at least one hidden in the snow nearby.
Defeat them and follow the path a short distance to the South. Be careful because there is a Riekling Rider waiting in this corridor. There are at least 3 more Rieklings waiting this corridor as well. Follow this path to the South. It will take a turn to the left and then lead into another open cavern.
In this cavern you will find another Riekling Camp. Either head over the ledge or go over to the left (North) and follow the slope down.
Once in this lower portion, turn to the South and head toward the bridge there. This leads into the active part of the camp in most cases. Expect one or two Rieklings to emerge from the snow in this area. There is likely on Riekling on the watch tower to the left of the foot of the bridge. Take your time moving forward if you are a stealth character or a ranged fighter. Otherwise, just go across the bridge and deal with the Rieklings.
In the next section of the camp to the South be wary of another Riekling Rider or two who will likely be hunting you with the rest of this part of the clan. Take your time fighting through this cluster of foes. Expect to encounter a few Bristleback Boars as well. Defeat them and head on through, looting what you can. Follow the path forward to the North from there. You will find the quick way back out to Solstheim that way.