We must never be seen

I got the SoulCrystal acheivment! Finally! Below I've made a guide on how to get it on singleplayer;

Step 1: Go to St. Petersburg (Russia Map)
Step 2: get a nightvision (ID 334)
Step 3: Go into the tunnels
Step 4: do @night
Step 5: Go to the very far right end of the metro tunnels where the rocks are collapsed
Step 6: Go up to the SoulCrystal rune/icon
Step 7: Put your back up against it and exit the world
Step 8: Load back in and you should be in a chamber with a blood red crystal
Step 9: Get a honey badger (ID 116) and lots of ammo (ID 6/100)
Step 10: Place a horde beacon by the crystal
Step 11: Stand behind the crystal and shoot every zombie that comes in
Step 12: You should have been teleported to a hospital, go to the very back and go right.
Step 13: Go all the way left to 2 robotic arms holding another blood red crystal
Step 14: Approach the crystal. It will give you the SoulCrystal acheivment and teleport you back to the first room with the crystal.

There you go, you got the SoulCrystal acheivment!