Elden Ring Sealed Tunnel is another optional dungeon in the Altus Plateau region and home of the Onyx Lord boss. The Sealed Tunnel is the only way to access the Divine Tower of West Altus in the video game developed by FromSoftware. In this Elden Ring guide, you will learn where to find the Sealed Tunnel, loot all the items, and reach the boss arena and the Divine Tower of West Altus.
Where To Find the Sealed Tunnel
The Sealed Tunnel can be found in the Altus Plateau region, behind the massive walls of Leyndell Royal Capital.
To reach the Sealed Tunnel, head directly east from the Outer Wall Phantom Tree Site of Grace until you reach the slope, splitting the shallow lake into two halves. Proceed down the slope to reach the lake and head to the south past the egg-looking enemies until you see the entrance.
Even if it appears to be a “Sealed” Tunnel, there is an imaginary wall next to the torch that, if attacked, will reveal the secret path. This path leads to the first room of the dungeon, where you will encounter several Scavengers who are busy mining.
Follow the path to the right, kill the resting Scavenger, and loot the corpse hanging on the edge of the wooden platform. Head back, down the slope, and past the wooden barrels and crates, you will find a chest containing Smithing-Stone Miner’s Bell Bearing.
Clear the bottom floor area and collect all the Smithing Stones  and Cracked Crystals from the cave’s walls. Behind the chest containing the Smithing-Stone Miner’s Bell Bearing, there is another illusory wall that, if attacked, will reveal the path further into the dungeon.
This path leads to a lift that you can use to go down. Once down, there’s another illusory wall at the end of the path, followed by another one with a corpse holding a Golden Rune  in front of it. You will reach a larger area with giant roots and wooden platforms that you can walk on.
On the platform to the right, there is a narrow tunnel leading to a corpse holding a Stonesword Key guarded by a Vulgar Militia enemy. On the roots going across, another corpse holds a Gold-Pickled Fowl Foot.
There is an Abductor Virgin in the pit below that you can try to lure out to break the statue with a glowing cut containing three Smithing Stones . After defeating the Abductor Virgin, loot the corpses on the ground to receive a Rune Arc, a Golden Rune , and three Furlcalling Finger Remedys.
There is also a Somber Smithing Stone  on the northwest wall for you to collect. Once you’re done in this area, climb the ladder and head through the east tunnel. Drop down through the narrow gap to the right, and you’ll encounter several Abnormal Stone Clusters that will start exploding as soon as you get close to them.
Loot the corpse beneath the stairs to receive 5x Grace Mimic and the one at the top to receive 2x Old Fang. To the northeast, there is another corpse behind a wheelbarrow holding 3x Large Glintstone Scrap. Head to the south and hit the illusory wall to reveal the path further into the Sealed Tunnel.
Drop down on the roots to reach the bottom floor and collect the Smithing Stone , 4x Lightning Grease, and a Golden Rune  that you will find on your way down. Follow the path to reach the boss arena, where you will face the Onyx Lord Boss.
Once you defeat the Onyx Lord Boss, you will receive 16.000 Runes and the Onyx Lord’s Greatsword. In the next area, you’ll find a Site of Grace and the entrance to the Divine Tower of West Altus. That’s everything you need to know to complete the Elden Ring Sealed Tunnel.