In this guide, you will find how to open the Blue Key card door in Sons of the Forest.
In order to get key cards, you will need to have a shovel. After getting it, make your way to the green ping that is closest to the beach and dig the hatch up to get the key card.
Get inside and there will be a lot of stuff including a 3D printer. You will find the maintenance key card near the computer terminal that will allow you to open up the blue doors. One of the doors leads you to Hydroponics.
There’s a second Blue Door in Hydroponics that requires a second key, you need to swim and there will be a door to the left. Swim into there and you will find a key card on the desk. You can use this key card to open up the door and get out of here.