Hello! Well this is kind of an old glitch but it still works just no one has tried it 1
1.go to the stairs next to tunnel
2. walk up the cement side of the stairs crouching
3.when it levels off fall off and into the wall
4. walk left still in the wall till u see a pole looking thing
5.walk toward the pole until don't see the wall to the right anymore
6. walk back toward the right gently walk into the wall
7. stand up and kill people walking up the tunnel and out of the tunnel.
Warning: may take several tries to get into the wall
Credits:whoever found the stairs glitch in the first place =)