After Nina went off in her bike, you must go to the right. You will need to enter to the room of the yellow worker.
1. Scare the cat using your mask.
2. Pick the key on the ground and use it with the lock on the ventilation access in the right.
3. Use the lock to lock the door and open the ventilation access. The cat will attack the worker, so he will open the window.
4. Enter through the now open window and once inside the kitchen, exit through the window above the oven at the left.
5. Outside you will see a waterfall below you. Pick the feather the bird drops and use it with the cat to open the way at the right.
6. Enter to the first entrance. Is the Nina's laboratory.
7. Once she ask you for a magnetron, exit the lab and go to the elevator at the right.
8. Once you return to the kitchen of before, take the magnetron from the oven and exit through the window above again.
9. Once outside again, let other achievement pops, then select the magnetron from your inventory and throw it to the waterfall below you.
Then, the achievement must pop.