Cave sulfur spawns in specific biomes, not randomly across the map

Cave sulfur is found only in certain underwater biomes in Subnautica, and it does not appear in the open ocean or shallow safe areas. The most reliable locations are the Dunes, the Grassy Plateaus deep caves, and the Kelp Forest caves. You will not find it lying loose on the seafloor — it grows as a yellow mineral deposit attached to cave walls and ceilings, which you harvest by swimming up to it and using your knife or a mining tool.

The reason cave sulfur matters is that you need it to craft batteries and explosives early in the game. Without knowing where to look, you can waste time exploring dead-end caves or biomes that do not contain it. This guide tells you exactly which caves hold sulfur and how to recognize the deposits when you find them.

Key Takeaways

  • Cave sulfur appears as yellow mineral deposits on cave walls and ceilings, not as loose items on the ground.
  • The Dunes biome has the most cave sulfur deposits and is the easiest location to reach early in the game.
  • You harvest sulfur by swimming close to the deposit and using your knife or a mining tool to break it off.
  • Grassy Plateaus caves and Kelp Forest caves also contain sulfur, but require more preparation and travel time.

The Dunes caves hold the most sulfur deposits

The Dunes biome is located to the west of your starting location (the Safe Shallows). To reach it, swim west from your pod until the seafloor drops away and the water becomes darker and more open. You will know you are in the Dunes when you see large rock formations and a sandy, sparse landscape with few plants. The caves in this biome are scattered across the area, and they contain more cave sulfur than any other location.

Once you enter a Dunes cave, look up and to the sides of the tunnel walls. Cave sulfur deposits are bright yellow and roughly the size of your fist. They stand out against the darker rock. Swim up to each one and use your knife (or a mining tool if you have crafted one) to harvest it. Each deposit gives you one sulfur. You can usually find three to five deposits in a single Dunes cave before you run out of air and need to return to the surface.

The Dunes are dangerous because aggressive fish like the Reaper Leviathan patrol the open water, but the caves themselves are safe if you stay inside and do not wander into the open biome. Bring a flashlight or a vehicle with lights so you can see the deposits clearly.

Grassy Plateaus caves require deeper exploration

The Grassy Plateaus biome surrounds your starting area to the north and east. The caves here are smaller and more maze-like than the Dunes caves, but they do contain cave sulfur. To find them, swim north or northeast from your pod and look for cave entrances in the cliff faces and rock formations. The entrances are often dark openings that drop downward into the rock.

Inside Grassy Plateaus caves, sulfur deposits are scattered throughout the tunnels, but you will need to explore deeper and longer to find them. These caves are also home to smaller aggressive fish like the Crashfish, which will attack you if you get too close. Bring a knife or a stasis rifle (a tool that freezes enemies temporarily) if you plan to spend time here. The sulfur deposits themselves are the same bright yellow color as in the Dunes, so the harvesting process is identical.

Kelp Forest caves are harder to reach but worth the trip

The Kelp Forest biome is located to the northwest of your starting area, past the Grassy Plateaus. It is a dense forest of tall kelp plants that block your view and make navigation confusing. The caves here are deep and require you to swim through narrow passages, so bring a small vehicle like the Seamoth if you have one. The caves contain cave sulfur, but you will need to explore carefully because it is straightforward to get lost in the tight tunnels.

The advantage of Kelp Forest caves is that they are less dangerous than the Dunes — there are no Reaper Leviathans patrolling nearby. The disadvantage is that the caves are harder to navigate and take longer to explore. If you are just starting out and need sulfur quickly, the Dunes are a better choice. Save the Kelp Forest caves for later when you have better equipment and more experience navigating tight spaces.

Use a mining tool to harvest sulfur faster than a knife

Your knife works to harvest cave sulfur, but it takes several hits to break off each deposit. A mining tool breaks deposits in one or two hits and is much faster. You craft a mining tool in your fabricator using titanium and a diamond. Since diamonds are rare early in the game, you might not have a mining tool right away — in that case, your knife is fine for now.

If you do have a mining tool, bring it with you on every cave run. You will harvest sulfur in half the time, which means you can collect more deposits before your oxygen runs out. The mining tool also works on other mineral deposits you will encounter later, so it is worth crafting as soon as you have the materials.

Bring a flashlight and plan your air supply

Cave sulfur deposits are in dark tunnels where your suit's built-in light does not reach far. Bring a flashlight (crafted from a battery and a quartz crystal) so you can see the yellow deposits clearly. Without a flashlight, you will miss deposits and waste time swimming around in the dark.

Plan how long you can stay in a cave based on your oxygen tank. A standard oxygen tank gives you about 45 seconds of air. If you are exploring a cave that is 30 seconds away from the entrance, you have only 15 seconds to harvest sulfur before you need to turn around and swim back. Bring a larger tank or multiple tanks if you want to explore deeper. You can also craft a high-capacity oxygen tank once you unlock the blueprint, which gives you more time underground.

Mark cave locations on your PDA so you can return later

Once you find a cave with cave sulfur, use your PDA (personal data assistant) to place a waypoint at the entrance. Open your map, click on the location, and add a marker with a custom name like "Dunes Sulfur Cave 1". This way, you can return to the same caves later without having to search the entire biome again. You can place multiple waypoints across different caves so you have several sulfur sources to choose from.

As you progress in the game and unlock better equipment, you will be able to explore caves that were too dangerous before. Marking locations now means you can come back and harvest more sulfur whenever you need it, without wasting time on exploration you have already done.

Frequently Asked Questions

Can I find cave sulfur in the Safe Shallows?

No. Cave sulfur only spawns in the Dunes, Grassy Plateaus, and Kelp Forest biomes. The Safe Shallows caves do not contain it. If you are looking for sulfur, you must travel to one of those three biomes.

How much cave sulfur do I need for batteries?

A standard battery requires one copper ore and one cave sulfur. If you plan to craft multiple batteries, you will need several sulfur deposits. Most players collect 10 to 15 sulfur early on so they have enough for batteries and other crafting recipes that use sulfur.

What do I do if a cave deposit is too high to reach?

Some deposits spawn on high ceilings where you cannot swim up to them. If you cannot reach a deposit after trying, leave it and move on. There are always more deposits in other caves. Do not waste oxygen trying to reach something that is out of reach.

Do I need a vehicle to get cave sulfur?

No. You can swim to all three biomes on foot and explore caves without a vehicle. A vehicle like the Seamoth makes travel faster and safer, but it is not required. If you do not have one yet, just swim carefully and bring extra oxygen tanks.

Will cave sulfur respawn if I harvest it all?

No. Once you harvest a deposit, it does not come back. However, there are many deposits across multiple caves, so you will not run out. If you need more sulfur later, explore caves you have not visited yet or return to caves you marked earlier to see if you missed any deposits.