The game will allow you to investigate the shelter after you eliminate all four targets. This happens because once you investigate it, you will have to use a passage and end the mission. This is how you should infiltrate the shelter:
Reaching the shelter
Before you get to the shelter, you should prepare yourself. If you have not investigated the basement of the main house yet (M7.36), you should unlock your way. Doors that lead to the basement are closed (M7.31) (M7.32). Thus, you will have to use the crowbar or the basement key. The key is located in a small garage, next to the house (M7.11). However, it's much easier to obtain it after you kill Ezra Berg (search his body).
Unfortunately, unlocking the door to the basement is not all. Now you need to pass the face scanner (M7.37). The easiest solution is to obtain a mask. In order to do that, head to the upper floor of the main house and locate the room with a 3D printer (M7.17). Wait for one of the hackers to leave the room and launch the printer. Leave the room, wait for the printer to finish, and only then get back to the room to collect Sean Rose's face mask. Take the mask to the face scanner and use it to access the shelter.
Remember - an alternative way to open the door would be to drag Rose's body to the face scanner. Unfortunately, this would be very tedious: not only would you have to eliminate Rose in the main house, but you would also need to eliminate all other soldiers on your way to the shelter.
Investigating the shelter
Once you get to the shelter, you will need to examine three interactive parts of the shelter - the large board, a small side board and the desk. Do this and the exit will be unlocked (M7.38).
Other exits located on the map
During "Freedom Fighters" you are obliged to use the exit located in the shelter BUT during optional contracts and escalations, you can use other exits. These exits are:
- South gate (M7.39)
- Front gate (M7.10)
- The bridge (M7.11)
- The river (M7.12)
- Quad bike (M7.9) - you need Quad Bike Keys, located in a hut in the south (M7.4)