Sneak past the first few guards. Do not waste time on them: When you start the level, you have to jump a fence to get inside an alley. Run until just before the lights at the end of the alley, then continue crouched. Even if the guards spot you, there is no need to stop. Continue behind the fire to the ladder in the dark corner of the room. Once you are up, you can easily knock out the guard below by jumping on top of him. Then, continue and sneak past the two guards ahead. You have to time your sneak carefully. Once you get past them, use the same principle; move through the courtyard in the shadow up to the fence, then continue next to it to get inside the little yard in front of you. Once inside, leap down the manhole. Do everything previously described without stopping, except when you sneak past the two guards in the alley. If you are not in a particular hurry, you can also pick up the medkit after you knocked out the guard. It is located on the balcony on your right.