Climb the ladder at the opposite end of where you entered, go to the top. Continue toward the window til a wide section of floor is missing, look at the bricks on the right, jump to those, then jump to the next section of floor, climb in the window.
Climb the green ladder ...where you first enter the area and ...after you get rid of all the soldiers, continue to your right up to the next platform, then leap forward to next platform and walk to the end, which ends up to the right of the window. Face the window and leap to it, climb up and....Woila!! Good Luck! O