Subnautica’s Alien Arches are fixed teleporters, not a player-selected fast-travel menu. Each usable arch connects to one predetermined location. The most important links are the Alien Thermal Plant’s route from the Inactive Lava Zone to the Quarantine Enforcement Platform, the Floating Island–Mountain Island island pair, the four Alien Arch Caches that support ingredient runs to the Primary Containment Facility, and the two arches in the Sea Emperor aquarium.
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You activate an arch by placing an Ion Cube in its nearby terminal or pedestal when the structure accepts one. The Primary Containment Facility has an additional Blue Tablet requirement, and its aquarium arches become useful only after the endgame sequence has progressed. A Prawn Suit can enter these structures; follow the interaction prompt shown at the particular arch.
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How Subnautica’s Alien Arches work
Alien Arches are Precursor gateway structures with a bright green portal surface. They are fixed links: you cannot choose an arbitrary destination, dial a coordinate, or redirect one arch to another destination. The entrance determines where you arrive.
That makes every arch valuable for a different reason. Some shorten an island trip, some turn repeated Hatching Enzyme ingredient runs into manageable loops, and one provides a late-game shortcut from the deepest volcanic area to the surface-side quarantine facility. Treat them as permanent connections on the crater map rather than as a general teleport network.
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What you need before entering one
- Ion Cube: carry at least one for an arch whose terminal accepts a power item. The principal arch in the Alien Thermal Plant is explicitly activated with an Ion Cube.
- Blue Tablet: required to enter the Primary Containment Facility.
- Vehicle plan: the Prawn Suit can enter the arches. A large vehicle cannot simply be driven through every structure, so park it outside and use the vehicle suited to the chamber.
- Navigation aid: place beacons at remote entrances, particularly in the Lost River, Lava Castle, Lava Lakes and cache chambers.
Portal locations at a glance
| Portal or arch group | Location | Fixed destination | Activation and story gate | Best use |
|---|---|---|---|---|
| Alien Thermal Plant principal arch | Inside the Alien Thermal Plant in the Lava Castle, Inactive Lava Zone | Quarantine Enforcement Platform on Mountain Island | Insert an Ion Cube at the arch terminal; reaching the plant is a late-game progression step | Deep-zone escape and a fast route to the quarantine platform |
| Floating Island arch | Approximately -662, 2, -1050 |
Mountain Island arch | Activate the usable side with an Ion Cube | Fast travel between the two islands |
| Mountain Island arch | Approximately 340, 61, 903 |
Floating Island arch | Activate the usable side with an Ion Cube | Return route between the islands |
| Northwestern Mushroom Forest cache arch | Approximately -750, -239, 435 |
Primary Containment Facility area | Cache access and a powered arch interaction; carry an Ion Cube | Collecting ingredients for the Hatching Enzymes sequence |
| Crag Field cache arch | Approximately -81, -290, -1360 |
Primary Containment Facility area | Cache access and a powered arch interaction; carry an Ion Cube | Ingredient runs from the Crag Field |
| Ghost Forest cache arch | Approximately -931, -611, 991 |
Primary Containment Facility area | Cache access and a powered arch interaction; carry an Ion Cube | Ingredient runs from a very deep, difficult-to-navigate location |
| Bulb Zone cache arch | Approximately 1383, -296, 757 |
Primary Containment Facility area | Cache access and a powered arch interaction; carry an Ion Cube | Ingredient runs from the eastern side of the crater |
| Primary Containment Facility aquarium arches | Aquarium section in the Lava Lakes | One returns to the aquarium antechamber/moonpool route; the other leads to the Quarantine Enforcement Platform | Blue Tablet to enter the facility; progress the Sea Emperor sequence; bring spare Ion Cubes | Leaving the aquarium and reaching the surface-side endgame route |
The coordinates are map positions in the game’s usual X, Y, Z format. They are approximate, so use terrain, beacons and the surrounding biome to locate the chamber rather than expecting a marker to place you exactly on the arch.
1. Alien Thermal Plant principal arch
Where it is
The principal arch is inside the Alien Thermal Plant, a Precursor facility in the Lava Castle within the Inactive Lava Zone. Reaching the room means surviving the Lost River and volcanic zones, finding the Lava Castle and entering the facility itself. This is not an early-game portal.
Where it goes
The arch connects directly to the Quarantine Enforcement Platform on Mountain Island. It is the major deep-to-surface shortcut: instead of piloting all the way back through the Lost River and shallower biomes, you can emerge at the island facility once the arch is powered.
How to activate it
- Locate the principal arch and the terminal beside it inside the Alien Thermal Plant.
- Have an Ion Cube in your inventory.
- Use the terminal and insert the Ion Cube when the game presents the interaction prompt.
- Wait for the green portal surface to become active, then enter with the player or a Prawn Suit as the arch permits.
- On the Mountain Island side, place a beacon if you expect to use the route again; the island facility can contain several visually similar alien structures.
When this route is most useful
Power it before a long volcanic-zone expedition or before transporting materials out of the Lava Lakes. It is also a reliable retreat after collecting resources in the Inactive Lava Zone. The arch does not replace a base, storage plan or thermal-power setup, but it removes one of the most dangerous return journeys in the game.
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2. Floating Island and Mountain Island arch pair
Coordinates and connection
The crater map places one arch on the Floating Island at approximately -662, 2, -1050 and its partner on Mountain Island at approximately 340, 61, 903. These two island arches are connected to each other. They are the notable island-to-island exception to the cache arches that serve the Primary Containment Facility area.
Using the pair
- Reach either island arch and find its nearby activation pedestal or terminal.
- Insert an Ion Cube if the terminal is inactive and accepts one.
- Enter the green portal to arrive at the paired island.
- Mark both exits with beacons or a map note. Island approaches can be obscured by weather, cliffs and the surrounding ocean surface.
Activate the side that is convenient for your current base and travel pattern; once the pair is powered, the connection is useful in either direction. It is especially helpful when moving between island facilities without returning to the open-water route.
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3. Alien Arch Caches and the Primary Containment Facility
Four cache arches are distributed around the crater. Their practical role is ingredient collection for the Hatching Enzymes sequence: they provide shortcuts into the Primary Containment Facility area rather than forming a free-form chain among the biomes.
Northwestern Mushroom Forest cache
The arch is approximately at -750, -239, 435. The negative Y value indicates a deep chamber below the surface, and the surrounding Mushroom Forest terrain can make a direct approach difficult. Bring an Ion Cube, a beacon and enough supplies to complete the intended ingredient run before returning through the same route.
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Crag Field cache
The Crag Field arch is approximately -81, -290, -1360. It is part of the cache network linked to the Primary Containment Facility. Because the Crag Field is open and hazardous, establish your approach heading before descending and leave a visible beacon at the chamber entrance.
Ghost Forest cache
The Ghost Forest arch is approximately -931, -611, 991. This is one of the deepest listed cache locations. Plan the trip around vehicle depth, power and return oxygen rather than treating the arch as a quick sightseeing stop. A beacon is particularly valuable because Lost River vegetation and branching tunnels can hide the route back.
Bulb Zone cache
The Bulb Zone arch is approximately 1383, -296, 757. It serves the same Primary Containment Facility ingredient-run purpose from the eastern side of the map. Approach with a clear heading and enough inventory space for the materials you intend to collect.
What the cache arches do not do
These arches do not let you select another biome or jump directly among all four cache chambers. Each one has a fixed link to the Primary Containment Facility area. Use the cache nearest to the ingredient or route you need, then return through its paired connection.
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4. Primary Containment Facility aquarium arches
Entering the facility
The Primary Containment Facility is in the Lava Lakes and is the final major story location. A Blue Tablet is required to enter. Bring additional Ion Cubes: the incubator and portal interactions can consume or require them, and running out after a long descent can force a hazardous return trip.
The aquarium route
The aquarium section contains two arches. One returns toward the aquarium antechamber and moonpool route; the other leads to the Quarantine Enforcement Platform. Their value is tied to the Sea Emperor sequence, so reaching the room does not necessarily make every interaction immediately available.
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Treat the aquarium as a story-critical laboratory, not merely as a transit room. Follow the Sea Emperor objectives and complete the required sequence before expecting the aquarium teleporter to function as the final exit.
Using the aquarium arches
- Enter the Primary Containment Facility with the required Blue Tablet.
- Progress the Sea Emperor sequence far enough to unlock the relevant aquarium interactions.
- Check each arch’s terminal and insert an Ion Cube when prompted.
- Use the antechamber or moonpool-side arch when you need to return into the facility route.
- Use the Quarantine Enforcement Platform arch when the story has made that surface-side destination the correct next step.
Keep spare Ion Cubes in your inventory before activating the final arch. The teleporters are fixed, so confirm the destination associated with the arch you are standing in instead of assuming both aquarium structures lead to the same place.
How to activate and travel through any portal
- Find the structure. Use the coordinate ranges above as a search area, then identify the alien chamber and its bright green arch.
- Search for the terminal. The pedestal or control point is normally next to the arch, not at the far end of the room.
- Check the progression gate. A missing Blue Tablet, an unopened facility or an incomplete Sea Emperor sequence can prevent the interaction even when you have an Ion Cube.
- Insert the Ion Cube. Select the terminal and place the cube only when the game displays the appropriate prompt. Do not discard cubes elsewhere and assume the portal will power automatically.
- Wait for activation. The portal surface changes to a usable green gateway. If no prompt appears, inspect the pedestal again and verify that the structure is the correct arch.
- Enter carefully. The Prawn Suit can enter these gateways. Approach straight on, follow the current interaction prompt and avoid trying to force a larger vehicle into a narrow opening.
- Mark the exit. Drop a beacon on the destination side and record which fixed link it represents. This prevents confusion when several alien facilities are nearby.
Recommended progression route
- Surface exploration: explore the islands and establish beacons before committing to a deep-zone expedition.
- Lost River: build a dependable route through the deep biome and identify a return path for your vehicle.
- Inactive Lava Zone and Lava Castle: reach the Alien Thermal Plant and prepare an Ion Cube for its principal arch.
- Alien Thermal Plant: activate the Quarantine Enforcement Platform connection. This is the most consequential portal unlock because it links the deep volcanic route with the island facility.
- Lava Lakes and Primary Containment Facility: obtain the Blue Tablet, enter the facility and advance the Sea Emperor sequence.
- Aquarium exit: bring spare Ion Cubes, activate the appropriate aquarium arch and use the fixed route to continue the ending sequence.
The cache arches can be visited whenever you are collecting the ingredients needed for the Hatching Enzymes. They are shortcuts for that objective, not mandatory replacements for every deep-zone route.
Preparation checklist for portal trips
- Power items: at least one Ion Cube; carry spares for the Primary Containment Facility.
- Access items: the Blue Tablet for the Primary Containment Facility.
- Navigation: beacons at both sides of every portal you intend to reuse.
- Depth and vehicle planning: confirm that your vehicle can reach the biome and that the Prawn Suit can be taken through the arch.
- Inventory space: leave room for Hatching Enzyme ingredients or facility materials.
- Emergency supplies: food, water, healing items and a return route; teleportation does not remove the hazards around either entrance.
- Story readiness: do not rely on an aquarium arch before advancing the Sea Emperor sequence.
Troubleshooting an inactive or confusing arch
The terminal shows no interaction
Check that you are at the arch’s actual pedestal, not a decorative alien panel. Then verify the story gate: the Primary Containment Facility requires a Blue Tablet, and aquarium functions depend on Sea Emperor progression. If the terminal still does not respond, confirm that you have an Ion Cube in the inventory.
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That is normal for this system. Arches are fixed links. Compare the structure with the location table and the beacon name you placed; you cannot redirect the gateway to a preferred island or cache.
The Prawn Suit will not enter
Line the suit up with the opening and use the interaction prompt rather than attempting to ram the gateway. Move nearby vehicles out of the approach path. If the game does not show a prompt, the arch may not be powered or the current story state may not permit that interaction.
You cannot find the return entrance
Remote cache and volcanic chambers are easy to lose in branching terrain. Use beacons at both ends, keep a written coordinate note and leave your vehicle facing the route home. The Ghost Forest and Lava Lakes deserve extra navigation preparation because their depth and tunnel layouts make a visual return unreliable.
Choosing the right portal for the job
| Your objective | Use this portal group | Why |
|---|---|---|
| Reach the surface after working in the volcanic depths | Alien Thermal Plant principal arch | It links the Lava Castle facility to the Quarantine Enforcement Platform. |
| Move between the two large islands | Floating Island–Mountain Island pair | These arches are directly paired for island travel. |
| Gather Hatching Enzyme ingredients | Nearest Alien Arch Cache | Each cache provides a fixed shortcut to the Primary Containment Facility area. |
| Leave the Sea Emperor aquarium during the ending | Primary Containment Facility aquarium arch | The aquarium route becomes useful after the required story progression. |
Use the arch that matches the destination, not simply the one you discovered first. A beacon network and spare Ion Cubes turn the fixed-link design into predictable fast travel, while an unmarked portal can be more confusing than the original route.
Quick Recap
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