During the exploration in Sunless Skein mines, you come across a locked door on the left side of the Vestige point. This door leads to Lower Calrath and can be opened using the Sunless Skein Key in Lords of the Fallen.
To get this key, you need to pull some levers and go through narrow spaces, which can sometimes confuse you. But you don’t have to worry, as I will help you get to the Sunless Skein key in LOTF quickly.
Lords of the Fallen Sunless Skein Key location
From the Vestige of Hooded Antuli in Sunless Skein Mines, turn right and go down this tunnel. Keep following this path until you reach a closed door after passing a few enemies. Now, to open this door, turn left and climb up the ladder.
Keep going, and you’ll reach a metal door soon. Use an Umbral lamp to pass through. Continue running and jump down by breaking the weak wooden floorboards. Down here, find a tunnel that connects to the outside.
On this platform, use an Umbral lamp to reveal a bridge. Use this to go to the other side and go up a few sets of ladders. You’ll eventually reach the tunnels again. After the tunnels end, you’ll find more wooden platforms with a lever in Lords of the Fallen.
Pull it to open the door down below. Continue, and you’ll find another closed door. Avoid it, and to find another way, turn right, and you’ll find a small path on the side of the door.
Follow this path and pass through the steel door by using an Umbral lamp. Break the wooden door and use the Umbral lamp again, or turn to the umbral realm to pass through the steel door and jump down. Keep going through the long path until you reach the ladder.
Turn back to the real world and go up the wooden platforms. Keep going, and you’ll get to the area opposite the locked door in Lords of the Fallen. You can now open the door from this side.
Use the Ladder below the Umbral Stigma
Enter the Umbral realm again, go down the wooden path by the wall, and soulflay the umbral stigma. Jump down and climb up the ladder below the umbral stigma in Lords of the Fallen. Turn back to the real world and pull the lever.
Turn towards the tunnel and go through it. If you are on the other side for any reason, you can use the bridge that connects the other side to this one.
At the end of the tunnel, look for a ladder. Climb this ladder and break the wooden boxes at the top. Now turn to the umbral world or use the Umbral Lamp to see a bridge going to a box. The Sunless Skein Key is on top of this box in Lords of the Fallen.