Borderlands 4: Find All 3 Carcadia Burn Vault Key Fragments — Step-by-Step to Unlock and Beat Radix

The Carcadia Burn Vault — also called the Vault of Radix — is the second special dungeon in Borderlands 4 and it’s gated behind three key fragments. Below, you’ll find exactly where to grab each fragment, where the Vault door waits, and how to handle Radix, the Primordial Guardian you meet inside.

1. Carcadia Burn Vault key fragment locations
2. Carcadia Burn Vault door location
3. How to defeat the Primordial Guardian Radix

Carcadia Burn Vault key fragment locations

There are three key fragments you must collect before the Vault will open. Each fragment is in a different region of Kairos, and each one is straightforward to reach if you know the nearest fast travel point.

Fragment #1 — Yawning Yard (Lopside)

Fast travel to the Makeshift Chalet Safehouse, then head south to a building with a long upper corridor. Climb into that corridor and look for a dinner table; the first fragment sits in the middle of the table. Quick and simple.

Fragment #2 — Wreck of the Last Great Hope (Tonnage Peel)

Start from the Lowrise Safehouse area and go west toward the wreck. Enter the underground tunnels through the southern entrance, then take a right into a short red-lit corridor. Use your grappling hook on a small floor door to drop into a cave where the second fragment is hidden.

Fragment #3 — Ruined Sumplands

Fast travel to the Judgement’s Lapse Silo and head north into the Ruined Sumplands. On the lower level, find the body of water, then go northwest along the shore. Look for golden spheres in the wall; the third fragment is tucked below one of them.

Carcadia Burn Vault door location

After you have all three fragments, fast travel to the Grindstone of the Worthy region using the Rustical Hurl Silo (if unlocked). The Vault altar is north of the silo near the Vault icon’s blue circle. Move toward some debris on the region’s northwest side and the hidden altar will emerge as you approach.

How to defeat the Primordial Guardian Radix

Radix is a mobility- and awareness-focused fight. It puts pressure on your movement resources, so manage your dash/glide charges carefully. Also, Radix has an energy shield that takes extra damage from electricity-based attacks, so bring some shock weapons if you want to break the shield faster.

Small pangolins spawn constantly during the fight. They don’t do heavy damage, but they’re persistent and useful as easy targets if you get downed. Additionally, the boss operates at two levels above you, so its damage and health scale with your level.

Flying rocks

Radix slams the ground and kicks up floating rocks that block direct access. Later, the rocks’ radius expands toward the arena edges. Keep moving and use the rocks as temporary cover.

Shockwave

Radix often follows the pillar attack with a sequence of four electric shockwaves that sweep the arena. The safest place is atop one of the flying rocks created by the boss. If you’re on a rock, you can avoid the ground waves more easily.

Shooting rock

Occasionally Radix charges a rock with electricity and fires it at your current position. Dash or sidestep when you see the boss lift its left arm to avoid the projectile.

Jump attack

Radix can dig underground and then leap to land on and around your location. Keep lateral movement ready — run or dash sideways to dodge the impact and the area damage that follows.

Underground attack

When Radix goes subterranean and moves around, it often leaves a trail of bombs. Watch the ground and avoid the trail; the boss rarely resurfaces exactly where you stand, so staying mobile makes this easy to handle.

Tempest

Radix may charge at the center of the arena and summon lightning strikes across several points. Blue marks appear on the ground where lightning will hit. Move out of marked zones quickly; dash only if you still have charges, because conserving them for surprises is important.

Overall tips: prioritize electric damage to strip the shield, keep dash charges for emergency escapes, and use the flying rocks for both cover and a stable platform during shockwaves. After the fight, Radix drops weapons, Eridium, and cash, plus two red chests before you exit.

We defeated Radix at level 40 in Ultimate Vault Hunter Mode rank 2 and earned 2,552 XP for the kill. Also, completing the Carcadia Burn Vault for the first time grants a backpack upgrade that reduces regen delay.