The Investigate the Tadpole Pens mission is Subnautica 2’s first real puzzle that does not hold your hand. You will arrive at the facility, find a locked door, and quickly realise the keycode is nowhere near the building itself. The good news is that once you know where to look, the whole quest becomes much more manageable. Here is everything you need to get through the Tadpole Pens from start to finish.
Before You Head Out: What to Bring
This trip takes you deeper than anything before it, so packing correctly makes a real difference. Do not skip preparation here, because the Hot Caves will punish a poorly equipped Pioneer fast.
| Item | Why You Need It |
| Food and water | Standard survival for any long dive |
| Air Bladder | Emergency oxygen for the deep swim section |
| Distraction Flares | Useful against aggressive fauna on the route |
| Fully charged scanner | Plenty to scan inside the Pens |
| Basic Air Tank (minimum) | Required; advanced tank not essential |
| Heat Tolerance Adaptation | Mandatory, see below |
One critical step before you attempt this mission: you must unlock the Heat Tolerance Adaptation first. You get this by clearing the Angel Comb located 200 metres northwest of the Lifepod at bearing 300 degrees. Use the Sonic Resonator to destroy the viral flowers there. Without this adaptation, the hot biome around the Tadpole Pens will kill you on arrival, regardless of whether you are in a Tadpole or swimming. Several players have lost their Tadpole vehicle this way by heading over too early.
Also open your character menu and enable all landmark signals before leaving. This makes navigation significantly easier throughout the mission.
How to Reach the Tadpole Pens
Once you have the Noetic Advisor alert named “Tadpole Pens” and have listened to it to start the Investigate the Tadpole Pens mission, you are ready to move.
Starting from the Lifepod, swim 690 metres east. You do not need to dive down until you are directly above the signal. As you approach, look for the oxygen tunic on the near side, which is a small blue plant that releases oxygen bubbles. It sits in a gorge opposite the building entrance. Touch the bubbles to top up your oxygen before heading inside.
Inside the Tadpole Pens, head left and press the red button in the corridor. The door will not open, because a keycode is required. Head back to the oxygen tunic before you run out of air.
Where to Find the Tadpole Pens Keycode
The keycode does not exist anywhere inside the Tadpole Pens itself, so do not waste time searching the facility. A few minutes after pressing the red button, your Noetic Advisor will send another alert that reveals the location of Zip’s Blackbox. Interacting with Zip’s Blackbox is what grants you the Kurul Level Access Key, which transfers automatically to your PDA.
You can return to your Noetic Advisor to receive the Zip Blackbox signal formally, but you can also follow the directions below directly from the Tadpole Pens if you prefer not to swim all the way back.
How to Reach Zip’s Blackbox: Step by Step
Starting from the Tadpole Pens, here is the full route:
- Swim southwest approximately 210 metres, heading on a bearing of around 195 degrees. Replenish your oxygen at the oxygen tunics you encounter along the path.
- Follow the ravine south. Lava pipes run overhead through this section, so keep an eye on them as a landmark.
- Look for a cave entrance in the ocean floor as the ravine drops off. Drop down into it.
- Inside the cave, take the glowing blue tunnel entrance to the southwest and continue descending.
- You will reach a large cavern with a big lava vent at its centre. Move down and to the right side of this chamber to find a small cave opening.
- Exit your Tadpole vehicle here. The passage ahead is too narrow and the pressure will crush the vehicle if you go deeper. Leave it at this point and swim the rest.
- Swim down to the bottom of the cave ahead. You are looking at around 310 metres depth for this final section.
- On the large purple root at the bottom, you will find Zip’s Blackbox. Look for the small human hologram marker above it to identify the correct one. There may be another blackbox in the same chamber, but only Zip’s gives you the keycode.
- Interact with Zip’s Blackbox. The access key saves to your PDA automatically.
Important: Do not leave the cave before interacting with Zip’s Blackbox specifically. Interacting with the other blackbox in the same chamber will not clear the quest marker or grant the keycode.
Alternatively, if you are navigating from the Lifepod rather than the Tadpole Pens, swim 350 metres southeast, passing Chap’s Blackbox. At the cliff edge, swim down, use the oxygen tunic, then descend through the large hole beside it. Continue north-northeast and take the first tunnel on your right into the large lava vent cavern, then proceed as above.
How to Complete the Mission
With the Kurul Level Access Key on your PDA, return to the Tadpole Pens and press the red button again. The door opens this time. Behind it you will find a room with breathable air and a Noetic Advisor unit. Interact with it to work through the dialogue and unlock the waypoint for the next story objective.
The room beyond the door also contains scannable objects including a Repair Tool blueprint, so take your time inside once you are through. The Hot Cave itself is worth revisiting after the mission wraps up, as it contains additional resources, flora, and fauna to scan, plus a supply crate near Zip’s Blackbox that you may have missed during the rush to grab the keycode.
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