Mortal Shell 2: Crumbling Tunnel Walkthrough and Location

The Crumbling Tunnel is a short dungeon in Mortal Shell 2 that exists for one reason. It hands you the map that marks where Proxima’s signature sidearm, the Triarch Repeater, can be found. The catch is that reading the map slab triggers a cave-in, so you need to collect everything else first and then sprint out before the ceiling drops.

Quick answer: Enter through the portal-like opening in the Shattered Beacon area where you got the Proxima Shell, ride the elevator down, grab Ventrium and Laterite along the tunnel, then read the map slab at the dead end to reveal the Triarch Repeater search area. The tunnel collapses the moment you read it, so run straight back to the elevator to leave.

Crumbling Tunnel location and how to reach it

The entrance sits inside the Blackridge Cliffs, just east of the Shattered Beacon where you claim the Proxima Shell. If you are traveling on foot, set off from the Blackridge Pass beacon and cut through the cliffs toward the cave mouth. The overworld route runs through open ground with flying enemies, so keep a sidearm ready.

Player aiming a sidearm at a flying enemy with the Fire prompt on screen — Clearing the flying enemies on the way to the Blackridge Pass beacon using the sidearm. Image credit: Cold Symmetry

Push through the cliffs and you will meet a larger ground enemy near the path. Deal with it, then look for the cave opening that leads down into the tunnel. Stepping inside brings up the Crumbling Tunnel dungeon label on the map.

Armored character advancing on a spear-wielding enemy in the Blackridge Cliffs — Fighting through the cliffs enemy that guards the approach to the cave entrance. Image credit: Cold Symmetry

Full Crumbling Tunnel walkthrough

Enter through the portal-like opening in the Shattered Beacon area and follow the path to the wooden elevator at the end. Ride it down to reach the tunnel floor.

Crumbling Tunnel location title appearing as the character enters the cave — The Crumbling Tunnel name appears as you move into the cave and reach the elevator down. Image credit: Cold Symmetry

Crouch through the low opening below and clear the enemies waiting ahead, including a shield-carrying Brigand and a pair of Wretches. Break any wooden barriers that block the way.

Check the area to the left to pick up Ventrium from the growth there. This is a crafting material, so grab it before moving on.

Character moving through a narrow rocky cave passage toward a lit opening — Working through the tunnel passage while breaking barriers and dealing with the crawling enemy. Image credit: Cold Symmetry

Continue forward and watch for falling rocks. You can hang back and let the debris damage the Wretch ahead, or use ranged attacks. Collect the Laterite from the nearby growth once the path is clear.

Head into the dark cave to the left and follow it to the dead end. Shoot the explosive jars blocking the way to expose the map slab underneath.

Interact with the slab to read the Map of Triarch Repeater. This adds the sidearm’s search area to your world map, and it also triggers the collapse, so be ready to move immediately.

Escaping the collapse

As soon as you read the map slab, the tunnel starts to cave in and rocks begin dropping from the ceiling. Turn back toward the lit end of the cave and run for the elevator. Falling debris is telegraphed by small trickles of dust and pebbles from above, so avoid those spots as you go.

Character advancing through the rocky cave toward a bright opening during the collapse — Retracing the tunnel toward the lit exit while dodging falling rocks after reading the slab. Image credit: Cold Symmetry

A stray enemy may appear on the way out. You do not need to fight it, so run past and keep heading for the elevator. Ride it back up and leave through the entrance you came in from.

Sword-wielding character facing a glowing-headed armored enemy on a wooden platform — Handling the last enemy near the elevator before riding back up and exiting the cave. Image credit: Cold Symmetry

Note: Once the collapse finishes, the passage is sealed for good and you cannot return inside. Collect the Ventrium and Laterite before you touch the map slab, since the slab is the point of no return.

Rewards and how to confirm 100% completion

The main prize is the Triarch Repeater Map, which reveals where Proxima’s signature sidearm can be found. The weapon itself is picked up later, so the map only marks its search area for now. Along the way you also secure two crafting materials.

What you get	Where
Ventrium	Growth on the left after the first group of enemies
Laterite	Growth near the falling-rock stretch
Triarch Repeater Map	Map slab at the dead end, behind the explosive jars

You know the run is finished when the Triarch Repeater search area shows up on the world map and the Crumbling Tunnel entry is marked complete on your map. If it still reads as incomplete, you either skipped one of the two materials or left before reading the slab. Since the tunnel seals after the collapse, the only fix is to make sure both pickups are in hand before that final interaction.