1. Head southeast toward the agency pickup: a crossbow, bolts, and nightvision goggles. It's behind the western entrance of the tunnel, near a parked truck. Across the valley is a sniper tower. Use the trees for cover and move quickly to avoid fire. Being spotted by a sniper does not raise a general alert and so does not count against a Silent Assassin rating, but move cautiously, because Agent 47 can be killed by a single sniper shot on Professional difficulty. There is a guard patrolling near the Agency pickup. Hide behind the corner of the building, and wait for the guard to approach the truck. When he turns around, creep out behind him and grab the equipment opposite, and then quickly return to cover behind the building. Or sedate him and take his clothes. While these won't fool the patrolling guards, they will nullify the threat of the snipers.
2. Go northwest, back amongst the trees and look for where the road curves. Position Agent 47 on the north side of a tree and wait for the one of the trucks to arrive. The truck stops on an incline, raising its rear. This prevents Agent 47 from climbing inside, so the truck needs to begin accelerating before he can climb in. Move too soon, and Agent 47 will be gunned down by the sniper, but wait too long and the truck will accelerate away. The trick is to wait by a tree and begin counting to five from the moment the truck stops, and then run for it. If timed correctly, the sniper will not have time to open fire. Once inside, move to the rear of the truck and wait.
3. The truck enters the western entrance of the tunnel and heads east. First, it turns right and heads south. Second, it turns left and heads east again. Immediately after the second turn, the truck momentarily stops. Jump out. Guard patrols are not entirely reliable; sometimes a guard in the tunnel will see Agent 47 in the truck and raise an alert. If this occurs, then try again. For reasons that are mysterious, skippng the agency pickup effects the guard patrols inside the tunnel, making it harder to pass through undetected.
4. After exiting the truck, turn left and look for a metal door beside a garage door. The garage door cannot be opened. Peek through the keyhole of the metal door and wait for a patrolling guard to enter and exit the room. When the guard is gone, enter the room and approach the door the guard exited from. Wait and listen for the sound of the guard using another door on the southeast corner of the adjacent garage. Enter the garage and crouch behind the crates in the northwest corner. The guard will reenter the garage, wander behind some crates in the southwest corner, and then exit through the northeast door. When the guard has left the garage, use the southeast door and climb the ladder in the next room.
5. The ladder deposits Agent 47 back on the surface, under cover of a small building. Run around the building to its right and, near the base of another sniper tower, take cover behind the trees. Do not dawdle, because stepping out from the building exposes Agent 47 to further sniper fire (if no disguise). Looking south, the valley turns eastward toward a dead end. Where it turns, a single guard is patrolling. Use the crossbow to kill him. To preserve the Silent Assasin rating, the guard must be killed with a single shot and no misses. If you have a disguise, you can take out your anaesthetic and let yourself be seen. The guard will run toward you and allow you go get behind him to sedate him. With the guard dead or sedated, follow the valley to the end, where another small building conceals a ladder.
6. Climb onto the ladder, but do not climb down. Wait for a guard to enter and exit the room below before climbing down. It's also possible to hide behind the door before he comes in and sneak ahead. The setup of the next garage and storage room is, excpeting the position of a few crates, the same as before. Enter the garage behind the guard and creep behind the crates stacked against the eastern wall. Wait for the guard to open the northeastern door and follow him quickly. Agent 47 must shadow the guard as he enters the next room, but slip off to the left through the north door and back into the tunnel. This requires precise timing and care to remain undetected.
7. Wait for a truck to approach heading east, and when it stops climb into the back. The truck will then proceed toward the eastern exit of the tunnel. As before, guard patrols are not entirely reliable; sometimes a guard will see Agent 47 in the truck and raise an alert. If this occurs, then try again. When the truck arrives back at the surface, it will momentarily stop. Climb of the truck and simply head south to the exit for a Silent Assassin rating.
Silent Assassin Method
This is a very annoying level and getting silent assassin will be tedious and difficult, however there are various ways to obtain it contrary to other more entertaining levels. There are three general ways to go about it:
-Above ground. Run through the treeline to avoid the sniper from seeing you. Do this running, there is a path that will allow you to get through unseen. Then get to the lone guard patrolling near the supply drop and sedate him. Take his clothes to nullify the threat of the snipers and run to the exit. Is it actually possible to do this without even alerting another guard thanks to the guard's fickle patrolling routines, but it will be difficult and tedious. For some reason, this results in a 85-90% stealth rating even though no one will see you?
-Through the tunnel. When the level starts, you see a truck right ahead of you. Unfortunately you can't get into this truck in time, but you can catch the next one without being shot by snipers. Wait for it (possibly pick up the crossbow at the supply drop while waiting)and enter the tunnels. It is possible that the truck will take you all the way to the exit, however it seems to stop indefinately at some points so the game might have prevented such a technique. It is possible though difficult to sneak past the guards at all points except the heavily guarded perimeter. Use a truck to get past there. You'll eventually get to the exit point this way as well.
-A combination of the above (as described above). Some parts of the tunnel might lend themselves well for parts of the trip where the valley is too difficult and visa versa. Especially the southern pass with the lone guard is useful here, though sneaking past him unseen can be impossibly difficult.