The essence of the achievement is that you need to explore all the caves. There are 10 caves in the game.
How to get the achievement:
After loading the save, you will find yourself in the last cave next to the open gate. To get the achievement, you need to enter this gate and go 10 more steps. That's all, your achievement!
Copy to C:\Users\*user name*\AppData\LocalLow\ SKS\TheForest\*number*\SinglePlayer\Slot1
SavеGame will replace the first slot! So if you have a save in the first slot, make a backup