If you are working through the main story in Subnautica 2, the “Investigate Tadpole Pens” quest is one of the more confusing missions you will encounter. The Noetic Advisor (NoA) sends you a signal to look into this underwater facility, but actually getting inside requires a keycode that is hidden deep inside a separate cave system. I spent a good amount of time swimming in circles before I figured out the correct path, so I put together this walkthrough to save you the frustration.
In this guide, I will walk you through every step of how to investigate Tadpole Pens in Subnautica 2 and get the keycode. I cover what you need to prepare, the exact route to the facility, where to find Zip’s Blackbox for the Kurul Level Access Code, and how to finish the quest. Whether you are playing solo or in co-op, this guide has you covered for 2026.
Table of Contents
Prerequisites: What You Need Before Investigating Tadpole Pens
Before you even think about heading to the Tadpole Pens, you need to have a few things sorted. Skipping these preparations is the number one reason players get stuck or die trying to complete this quest.
Heat Tolerance Adaptation Is Mandatory
The Tadpole Pens sit inside Subnautica 2’s hot biome, an area filled with thermal vents and scalding water. Without the Heat Tolerance Adaptation unlocked, you will take constant damage just from being in the area. I cannot stress this enough: do not attempt this quest without it. You unlock Heat Tolerance Adaptation by researching the Angel Comb and Sonic Resonator materials found earlier in the game. If you have not unlocked it yet, go back and gather those resources first.
Tadpole Vehicle (Highly Recommended)
The Tadpole vehicle is not strictly required, but it makes the journey far more manageable. The swim from your Lifepod to Tadpole Pens is roughly 680 meters, and that is a long distance to cover on lung power alone. The Tadpole gives you speed, oxygen storage, and protection from smaller predators along the route. Keep in mind that the Tadpole has a crush depth limit. Going too deep will start damaging the vehicle, so pay attention to depth warnings on your HUD.
Supplies to Bring
Here is what I pack before setting out for the Tadpole Pens:
- At least 3 filtered water bottles and 6 cooked fish for the round trip
- 2 spare batteries for your Scanner and any tools you rely on
- An Air Bladder for emergency surfacing if your oxygen runs low
- An upgraded Oxygen Tank (the highest tier you have crafted)
- A Rebreather if you have one, since you will be diving below 100m for extended periods
- A Wavemaker or Seaglide for faster swimming when you are not in the Tadpole
Enable Landmark Signals
One quick tip that most guides skip: open your PDA settings and make sure Landmark Signals are enabled. This causes key locations like Tailings Village and the Hot Cave entrance to appear on your HUD when you get close. It is a small toggle that saves you a ton of guesswork, especially when you are navigating the canyon system on the way to Zip’s Blackbox.
How to Find and Reach Tadpole Pens in Subnautica 2
The Tadpole Pens facility is located inside the hot biome, roughly 680 meters directly east from your Lifepod. You will find it at a depth of about 150 meters. The journey takes you through increasingly warm water, so if you start seeing thermal vents and your screen gets a hazy orange tint, you are heading in the right direction.
Step 1: Leave the Lifepod and Head East
Surface swim or pilot your Tadpole east from the Lifepod. Keep an eye on your compass to maintain a heading of roughly 90 degrees. Within the first 200 meters, you will pass through a transitional zone where the water temperature starts rising. This is normal. If you have Heat Tolerance Adaptation, you will not take damage here.
Step 2: Navigate the Thermal Zone
At around 400 meters east, you will enter the hot biome proper. Lava pipes run along the ceiling above you, and thermal vents dot the ocean floor. The water here has a distinctive reddish-orange glow. Stay at mid-depth (around 100-150m) rather than hugging the floor, since the heat is more intense near the vents. Look for the purple Titan Rockbore roots growing along the canyon walls. These are your visual confirmation that you are closing in on the Tadpole Pens area.
Step 3: Locate the Tadpole Pens Entrance
At approximately 680 meters east and 150 meters depth, you will spot the Tadpole Pens facility. It is a structure built into the canyon wall with a distinct industrial look. Swim inside and you will find a red button on the wall near the entrance. Press it. This opens the main chamber but reveals a locked door further inside. That locked door requires the Kurul Level Access Code, and the only way to get it is from Zip’s Blackbox located in the Hot Cave.
Step 4: Take Note of Your Surroundings
Before you leave the Tadpole Pens, take a moment to look around the antechamber. You will see Azum Jars and other containers scattered around, along with signs that this was once a functioning facility. The Noetic Advisor will give you some dialogue about the significance of the location. Once you have pressed the red button and seen the locked door, it is time to go find that keycode.
How to Get the Tadpole Pens Keycode (Zip Blackbox Location)
This is the part of the quest that trips up most players. The keycode is not anywhere near the Tadpole Pens itself. You need to find Zip’s Blackbox in the Hot Cave, which is a separate location roughly 300 meters away from the facility. The journey is significantly longer than previous black box trips in the game, so come prepared.
Two Route Options
You have two ways to reach the Hot Cave where Zip’s Blackbox is located:
Route A: From Tadpole Pens. If you are already at the Tadpole Pens, face the entrance and turn southwest. Set your compass to a bearing of about 195 degrees. You will swim through a ravine filled with lava pipes overhead. Follow this canyon system until you spot a cave opening on your left side.
Route B: From Lifepod. If you prefer to start fresh from the Lifepod, head approximately 540 meters east and then dive to 236 meters depth. You will find Tailings Village, a landmark area with structures and supply crates. From Tailings Village, continue descending. The Hot Cave is located below the village at roughly 310 meters depth.
I recommend Route A if you have already reached the Tadpole Pens since it saves time. Route B is useful if you died or need to resupply at the Lifepod before attempting the deep dive.
Navigating to the Hot Cave
From Tadpole Pens, swim on a heading of 195 degrees. The canyon walls here are narrow with lava pipes running along the ceiling. The water gets progressively hotter the deeper you go. If you took the Route A approach, you should see a large cave opening after about 300 meters of swimming. This is the entrance to the Hot Cave.
Inside the Hot Cave, the environment is a maze of tunnels and chambers. Stick to the main path and do not take side tunnels. You are looking for a small black box device sitting on a ledge or attached to a wall. The game will prompt you to interact when you get close enough. If you have Landmark Signals enabled, Zip’s Blackbox will appear as a marker on your HUD when you are within range.
Oxygen Management in the Hot Cave
The Hot Cave sits at around 310 meters depth, which means your oxygen drains faster than at shallow depths. Here are my top strategies for surviving the dive:
- Swim down in stages rather than diving straight to 310m. Stop at 150m and 230m to check your oxygen level.
- If you brought the Tadpole vehicle, park it at around 200m depth. It cannot safely go to 310m without risking crush damage, so you will need to swim the last stretch on foot.
- Use the Air Bladder only as a last resort for emergency ascent. It is faster than swimming up manually when your oxygen is critical.
- The Rebreather significantly slows your oxygen consumption at depth. If you have one, equip it before entering the Hot Cave.
- If you are in co-op, have one player stay at a shallower depth with spare oxygen tanks so they can drop them for you if needed.
Interacting with Zip’s Blackbox
Once you locate Zip’s Blackbox in the Hot Cave, swim up to it and press your interact button. Your character will play an animation, and the Blackbox will give you the Kurul Level Access Code. This is the keycode you need to open the locked door back at the Tadpole Pens. The code is automatically added to your PDA, so you do not need to memorize it or write it down.
The Blackbox also contains lore about Zip, a missing colonist who was stationed at the Tadpole Pens facility. Listening to the full audio log is optional but adds meaningful context to the story. After you have the code, start making your way back to the surface. Ascend slowly to conserve oxygen, and return to the Tadpole Pens location.
Returning to Tadpole Pens and Completing the Quest
With the Kurul Level Access Code in your PDA, swim back to the Tadpole Pens facility. If you used Route A to reach the Hot Cave, simply reverse your bearing and swim northeast back through the canyon. The Tadpole Pens entrance should be easy to find again since you have already been there.
Opening the Locked Door
Enter the Tadpole Pens and approach the locked door you discovered earlier. The interaction prompt should now display the option to enter the keycode. Press your interact button and your character will use the Kurul Level Access Code to unlock the door. It swings open and reveals the inner chamber of the facility.
Inside the inner chamber, you will find more lore objects, supply crates, and the NoA Terminal. The terminal is your primary objective. Swim up to it and interact with it to upload your findings to the Noetic Advisor.
NoA Terminal Interaction
Interacting with the NoA Terminal triggers a dialogue sequence with the Noetic Advisor. The Advisor processes the data you collected from Zip’s Blackbox and the Tadpole Pens facility. This dialogue reveals important story information about what happened to Zip and the broader mystery surrounding the colony. Pay attention to the conversation because it ties into future quests.
After the dialogue ends, the quest marker updates and the “Investigate Tadpole Pens” objective is marked as complete. You will receive story progression and potentially unlock new areas or signals on your map. The facility itself can be freely explored after completion, so feel free to loot any remaining supply crates before you leave.
Common Mistakes to Avoid When Investigating Tadpole Pens
After reading through dozens of forum posts and Reddit threads about this quest, I noticed the same mistakes coming up over and over. Here are the most common ones and how to avoid them.
Skipping Heat Tolerance Adaptation
This is the biggest mistake players make. The hot biome deals constant damage if you do not have Heat Tolerance Adaptation. Some players try to brute-force it by packing extra medical kits, but the damage ticks faster than you can heal. Unlock the adaptation first. It takes a bit of extra time to gather the Angel Comb and Sonic Resonator, but it saves you from dying repeatedly.
Running Out of Oxygen in the Hot Cave
The Hot Cave is deep, and the swim there is long. Many players underestimate how much oxygen they need for the round trip. Always bring an upgraded oxygen tank and a Rebreather. Check your oxygen gauge frequently during the descent, and turn back if you drop below 30 seconds of air. It is better to make two trips than to drown and lose your progress.
Taking the Tadpole Too Deep
The Tadpole vehicle has a crush depth, and the Hot Cave goes well beyond it. Players who try to pilot the Tadpole all the way to Zip’s Blackbox end up with a damaged or destroyed vehicle. Park the Tadpole at around 200 meters depth and swim the rest of the way. This keeps your vehicle intact for the return trip.
Getting Lost in the Canyon System
The canyon between the Tadpole Pens and the Hot Cave has several branching paths. If you take a wrong turn, you can end up in a dead-end chamber with no landmarks. Enable Landmark Signals in your PDA settings before you start, and stick to the main canyon rather than exploring side tunnels. The correct path is the widest passage with lava pipes above you.
Not Bringing Enough Batteries
Between your Scanner, Seaglide, and other tools, battery drain adds up fast on this quest. Bring at least 2 spare batteries. The last thing you want is a dead Seaglide when you are trying to surface from 310 meters with 15 seconds of oxygen remaining.
FAQs
How to access tadpole pens in Subnautica 2?
To access the Tadpole Pens in Subnautica 2, swim 680 meters east from your Lifepod to a depth of 150 meters in the hot biome. You need Heat Tolerance Adaptation to survive the thermal environment. Once inside, press the red button to open the main chamber, then find Zip’s Blackbox in the Hot Cave to get the Kurul Level Access Code for the locked door.
How to get tadpole in Subnautica 2?
You get the Tadpole vehicle by crafting it at a Vehicle Bay using resources gathered during early exploration. The blueprint unlocks through natural story progression. You will need specific materials like Titanium, Lubricant, and Power Cells to build it.
Where to find tadpole in Subnautica 2?
The Tadpole Pens facility is located 680 meters east from the Lifepod at a depth of 150 meters inside the hot biome. Look for the purple Titan Rockbore roots along the canyon walls and the industrial structure built into the wall. Enable Landmark Signals in your PDA to make it easier to spot.
How deep can the Tadpole go before being crushed?
The Tadpole vehicle has a crush depth that sits around 200 to 250 meters depending on whether you have installed depth upgrades. Beyond that depth, the vehicle takes structural damage that will eventually destroy it. For the Hot Cave section at 310 meters depth, park the Tadpole at a safe depth and swim the rest of the way.
Do I need co-op multiplayer to complete the Tadpole Pens quest?
No, you do not need co-op multiplayer to complete the Tadpole Pens quest. The entire investigation can be done solo. However, playing in co-op has advantages: one player can carry spare oxygen tanks and wait at a shallower depth to provide emergency supplies during the deep dive to Zip’s Blackbox.
How to build tadpole in Subnautica 2?
To build the Tadpole vehicle, you need the Tadpole blueprint (unlocked through story progression) and a Vehicle Bay. Gather the required crafting materials including Titanium, Lubricant, and Power Cells, then interact with the Vehicle Bay to construct it. The exact material list may vary based on your game version.
Wrapping Up the Tadpole Pens Investigation
Figuring out how to investigate Tadpole Pens in Subnautica 2 and get the keycode is one of the more involved quests in the game, but it boils down to a straightforward process. Prepare with Heat Tolerance Adaptation and supplies, reach the facility 680 meters east at 150m depth, press the red button, then swim southwest on a 195-degree bearing to find Zip’s Blackbox in the Hot Cave at 310 meters depth. Grab the Kurul Level Access Code, return to the locked door, and interact with the NoA Terminal inside to complete the quest.
After finishing this quest, the Noetic Advisor will unlock new story leads and signals for your next objectives. The area around Tadpole Pens is rich with resources like Gold and Lithium, so it is worth making a return trip later if you need crafting materials. Keep exploring, upgrade your Tadpole for deeper dives, and enjoy the rest of Subnautica 2’s story.