Instructions
Go to the right from your prison cell. Save first.
Go up the first staircase. Two enemies will block your path; they are only vulnerable to attack when they turn their shields aside.
Go up the upper right staircase.
Cross the bridge into the next chamber. Hide in the alcoves when the guard looks at you and move toward him when his back is turned. Press "A" behind him to deliver a one-hit kill without having to battle. You'll get a Mid Tonic for your Solid Snake impression.
Go north into a similar passageway leading to the left. A guard is blocking the staircase, so repeat the same tactic on him.
Go up the staircase, defeat the two shield enemies and take the upper left staircase.
Cross the bridge into the next cell block. Walk into the left hand cell and through the hole in the back wall.
Walk off the right side of the ledge, climb down and walk to the gap between the two ledges. Climb down this and walk in the door. You enter a similar prison cell with an open sewer grating/ladder. Collect the Shelter from the treasure chest and go down the ladder by pressing "A" next to it and pressing "Down" once you're on the ladder.
Collect 1,500 gold pieces and a Lode Sword from the two treasure chests.