Investigating the Tadpole Pens is one of Subnautica 2’s first big story puzzles which requires you to deep dive into a heat soaked expedition to cracked ruins and lava caves where you’ll need the heat tolerance trait, good oxygen and Zip’s black box to open the Pen’s sealed door. This guide shows the approximate coordinates and approach from the lifepod, where to find the keycode to open the pen’s sealed door and complete the mission.
Tadpole Pen’s Location

When you’ve obtained the Heat Tolerance trait after clearing out the virus area, the NoA terminal will identify a new signal which resides in the lava area. After that you need to head to the Tadpole Pens, to get there you need to travel east from the lifepod. When you try to investigate the tadpole pens, you’ll come across a door that leads to the pen’s NoA terminal, but the door is sealed and you need a key to unlock the door. Depending on some factors, you may or may not get a marker for the keycode location. And in my case, I didn’t get any marker so I had to search for the key myself.
Obtaining The Keycode


To obtain the keycode, head southwest from the Tadpole Pens and try to identify the cave shown in the above second picture. There’s an alien structure and an oxygen plant before the caves entrance.

Head inside the cave and dive deeper until you reach a big lava area which is shown in the above image.

After you reach the lava area, look for an entrance below these lava structures which leads you to a much deeper section.

In this section, you’re going to find the blackbox which contains the keycode on a purple root as shown in the above image.
Unlocking Pen’s Door

After you’ve obtained the keycode, head back to the Tadpole Pens and interact with the button outside the sealed door. The camera will scan you and will unlock the door.

Head upwards to the NoA terminal and interact with it, you’ll be given a few dialog options – keep interacting with the terminal until you’ve run out of options. This marks the end of this mission.
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