There are eight Polygon Testing Grounds to find in Atomic Heart. They present unique challenges that require skill and mastering the game's mechanics. However, you cannot simply enter the Testing Grounds; you must first open them. Here is how to open all Polygon Testing Grounds in Atomic Heart.
Atomic Heart - How to unlock all Testing Grounds
Polygon Testing Grounds 1
You must use a tower to hack a camera and unlock the doors to Testing Grounds 1. After you have done this, you can enter the Testing Grounds.
Polygon Testing Grounds 2
You must head to the hacking device and hack into a security camera near the testing grounds. Use this to unlock the door and enter Polygon Testing Grounds 2.
Polygon Testing Grounds 6
Like Testing Grounds 1, you must hack a security camera from a tower and open the doors to Polygon Testing Grounds 6. This will open the door and allow you to enter.
Polygon Testing Grounds 8
You must climb onto the building where Testing Grounds 8 is located. Use the device to hack into cameras around the area. You must disable the three devices that look like white ovals. This will open an elevator inside of the building and lead you to Testing Grounds 8.
Polygon Testing Grounds 9
To open Polygon Testing Grounds 9, you must first visit another facility. You can enter through a manhole cover in the town in front of the red building or swim up through the pipe in the lake. The facility has four boilers to place glowing orbs into through the tube systems. Once you do this, the Hawk will be free.
Head to the tower at the lake's edge and hack into a camera. Point it at the statue in town and open the door to Testing Grounds 9. The door is actually in the wooden shed to the statue's left. Take the elevator and enter the facility.
Polygon Testing Grounds 10
Directly next to the Polygon Testing Grounds 10 is a farmhouse. Use the cart to climb the roof and go through the second-floor window. Hack the device and look through a security camera at the pig sty. Open the door, and an elevator will reveal itself. Take this to reach Testing Grounds 10.
Polygon Testing Grounds 11
Polygon Testing Grounds 11 requires some legwork to enter. You must call down the Hawk for maintenance, then climb onto when it lands. Slide down the rope into the compound containing Testing Grounds 11. To the right of the locked door is a building containing a disc key you will need.
Unlock the door after grabbing the disc key and head to Polygon Testing Grounds 11. Insert the disc key and descend into the facility by the elevator.
Polygon Testing Grounds 12
To enter Polygon Testing Grounds 12 in Atomic Heart, head to the Hawk Station in this area. Keep going past it to the beach. Follow the cliffs along the left wall until you find a tunnel. Follow this to find an elevator that will take you to Testing Grounds 12.
For more information on Atomic Heart, check out Can you place markers on the map in Atomic Heart? and How to increase inventory space in Atomic Heart on Pro Game Guides.