Blue Tablet location in Subnautica: Alien Thermal Plant in the Lava Castle, Ion Cube + Kyanite recipe, and both uses at the Primary Containment Facility.
Subnautica Blue Tablet — Where to Find It and How to Use It
The Blue Tablet is the Precursor key card that gates the very end of Subnautica: a glowing blue slab found inside the Alien Thermal Plant in the Lava Castle, crafted from 1 Ion Cube + 2 Kyanite, and used twice — once to open the Primary Containment Facility's entrance, and a second time for the Moonpool room inside. Picking one up or crafting one also triggers a telepathic message from the Sea Emperor Leviathan, so it doubles as the story's "we know you're coming" moment. This guide covers the full route down, the exact recipe, both doors it opens, and what to do if you ever lose it.
Here's what you'll learn:
- Where the Blue Tablet is and how to get inside the Alien Thermal Plant
- The exact crafting recipe and when the blueprint unlocks
- Both uses inside the Primary Containment Facility (you need two)
- The Sea Emperor event and the achievement it feeds into
- How to recover if you lost your tablets and all your Ion Cubes
Official resources: Steam store page · Official Subnautica Wiki — Blue Tablet · Official Subnautica Wiki — Alien Thermal Plant · IGN Subnautica page
What Is the Blue Tablet?
The Blue Tablet is one of the three Alien Tablets the Precursors left behind (alongside the Purple and Orange Tablets), classified as Equipment with the internal ID precursorkey_blue. It's a small, cold slab with a blue light that illuminates a symbol "resembling an upper case 'H'", per the databank entry you get from scanning it. Its role is pure access control: the databank speculates the tablets served as security clearance for whoever built them, and mechanically that's exactly what they are — door keys for the endgame Precursor facilities.
Per the official Subnautica Wiki — Blue Tablet: "The Blue Tablet can be found in the Alien Thermal Plant, and is used to access the Primary Containment Facility. One Blue Tablet is needed to gain entrance to the facility, and a second one is used to unlock the Moonpool room."
Where to Find the Blue Tablet
The Blue Tablet is located inside the Alien Thermal Plant, the small Precursor power station built into the Lava Castle in the Inactive Lava Zone (coordinates -75, -1182, 5 on the official wiki). That puts it at roughly 1,180 meters deep, which means the depth-module chain has to come first: a Cyclops with Depth Module MK3 or a Prawn Suit with MK2 (1,700 m / 1,700 m), following the normal route Lost River → Inactive Lava Zone, which we cover step by step in our walkthrough guide and Active Lava Zone guide.
Inside the plant, the tablet is behind the first Purple Tablet door — one of two locked doors in the facility, both requiring a Purple Tablet. The Purple Tablet's own blueprint comes from scanning the broken tablet fragment at the Quarantine Enforcement Platform's land entrance on the Mountain Island, and it costs 1 Ion Cube + 2 Diamonds to craft. Most players arrive with a spare purple tablet already in hand from the Lost River leg of the story, but if you burned yours earlier, that's the detour.
The Alien Thermal Plant has two Purple Tablet doors and no way around them. If you used your Purple Tablet at the Disease Research Facility or the Quarantine Enforcement Platform and didn't craft a spare, you'll reach the bottom of the world and find the Blue Tablet locked away. Craft extras before the deep dive — the recipe is 1 Ion Cube + 2 Diamonds at any Fabricator.
Shortly after picking the tablet up (or after crafting one later), the Sea Emperor Leviathan contacts you telepathically — the game's way of acknowledging you've reached the endgame threshold. This is also the trigger for the "Fourteen Thousand Leagues Under the Sea" achievement route, which requires finding and entering the Primary Containment Facility in the Lava Lakes.
How to Craft Blue Tablets
The Blue Tablet blueprint unlocks the moment you pick up (or scan) the tablet in the Alien Thermal Plant. From then on you can craft as many as you want at any Fabricator:
| Ingredient | Amount |
|---|---|
| Ion Cube | 1 |
| Kyanite | 2 |
| Build time | 3 seconds |
- Kyanite is mined in the Lava Castle and Lava Lakes around 900–1,300 m — the full farming route is in our Kyanite guide. The Lava Castle itself has plenty of loose crystals right outside the Alien Thermal Plant.
- Ion Cubes are the rarer half of the recipe. The official wiki counts only 26 Ion Cubes collectible without the Prawn Suit's Drill Arm, but the Alien Thermal Plant contains an Ion Cube Pyramid (a drillable Large Ion Cube Deposit), and the Primary Containment Facility has more once you're inside.
The Ion Cube Pyramid inside the Alien Thermal Plant yields several Ion Cubes per chunk with the Prawn Suit's Drill Arm. Since you're already down at 1,180 m for the tablet, bring the drill and bank a handful of Ion Cubes so you never run short for tablets or Ion Batteries later.
What the Blue Tablet Opens
You need two Blue Tablets total to finish the game:
- The Primary Containment Facility entrance forcefield — your first tablet. The facility sits in the Lava Lakes beneath the Inactive Lava Zone; the full approach (including the antechamber, Egg Laboratory and the Sea Emperor's aquarium) is broken down in our Primary Containment Facility guide.
- The Moonpool room forcefield inside the facility — your second tablet, which opens the corridor leading to the Aquarium and the Sea Emperor herself.
So the standard flow is: pick up the free tablet in the Alien Thermal Plant, then craft the second one before or after the descent. Both ingredient types are abundant right where you are: kyanite on the Lava Castle slopes, Ion Cubes from the plant's pyramid.
What If You Lose Your Blue Tablets?
Because Ion Cubes are finite before the endgame, a small but recurring community panic is "I lost my tablet / used my Ion Cubes and now I'm stuck." The good news: it's never actually a softlock in the current game. The recovery path, confirmed across Reddit threads like this one:
- Mine the Ion Cube pyramid inside the Primary Containment Facility with the Prawn Drill Arm (or the one in the Alien Thermal Plant) for fresh Ion Cubes.
- Grab kyanite right outside the Lava Castle — it spawns loose on the seabed, no drill required.
- Craft your two Blue Tablets and carry on.
The official wiki also documents the one historical way this could break the game: in an early version, picking up the Blue Tablet didn't unlock the blueprint, which could make it uncraftable and softlock a playthrough — a bug since patched. In the current build, picking it up always unlocks crafting, and there are no permanently missable tablets.
Don't confuse the Blue Tablet with the Orange Tablet, which opens the Alien Thermal Plant's warp-gate room and is found much earlier, sitting on a desk in the Deep Grand Reef Degasi Seabase. Both are covered together in our Kyanite guide's FAQ, which walks through where each tablet lives.
FAQ
Where do I find the Blue Tablet in Subnautica?
Inside the Alien Thermal Plant in the Lava Castle (Inactive Lava Zone, roughly -75, -1182, 5), behind the first Purple Tablet door. You need a Cyclops MK3 or Prawn MK2 to reach it.
How do I craft a Blue Tablet?
1 Ion Cube + 2 Kyanite at any Fabricator (3 seconds). The blueprint unlocks when you pick up the tablet in the Alien Thermal Plant.
What is the Blue Tablet used for?
It opens the Primary Containment Facility: one for the entrance forcefield, one for the Moonpool room inside. It also triggers the Sea Emperor's telepathic contact.
Do I need more than one Blue Tablet?
Yes — two total: one for the facility entrance and a second for the Moonpool room. Craft the second after picking up the free one.
Can you lose the Blue Tablet and softlock the game?
No, not in the current build. If you run out of tablets and Ion Cubes, mine the Ion Cube pyramid in the Alien Thermal Plant or Primary Containment Facility with the Prawn Drill Arm and grab kyanite outside the Lava Castle. An old patch-era bug that could softlock the game was fixed.
Related Guides
- Subnautica Walkthrough — Full Story Progression
- Subnautica Primary Containment Facility — How to Get There
- Subnautica Kyanite — Where to Find It and Every Recipe It's In
- Subnautica Sea Emperor — Story Guide
- Subnautica Active Lava Zone — Entrances and Gear
Last updated: August 13, 2026.
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