After escaping from the ruins, you find a factory to the north.
Now go to the Factory up north.
Go Through the Factory
First, check the computer to turn off the laser. Fight the Acid (Crono's Slash works well), then go up the conveyor belt. Step on the right-hand green spot, and check the wall to go down.
Go down the ladder, then walk left and up to a door in the wall. Go into the door, and walk up and right, then keep pressing A to check for a chest (Mid Ether). Then go back down to the side-by-side ladders and take the left ladder down. Keep going left for a chest (Robin Bow).
Finally, go back to the two side-by-side ladders, and take the right one. Go into the door, but don't stand there too long or you get grabbed and tossed onto a conveyor above you. Walk left along the conveyor belt avoiding the robots. If a robot is coming at you, run the other way to safety. Open the chest along the way (Ether), and finally, when you're all the way to the left, go down and through the door. Then go up the ladder and through the door. The bugs are avoidable.
When the path splits, take the right path first, and open the chest (Mid Tonic) then go through the door. Open the chests (top: 400G; bottom: Mid Ether), then check the computer. Now leave and go left, and into the room.
Open the chests to the left (top: Shelter; bottom: Ether), then exit bottom left.
Step forward, and when you hear the tone, press X A. Step forward again, and this time press B B.
Now go back up, and exit bottom right. Go down the ladder, and head left, through the door. Open the chest (Bolt Sword) then check the computer. Now leave.
Go back up the elevator, then head left (go slowly, the monsters will move but won't attack if you don't touch them) and ride the left-hand elevator.
Use the save point if you wish, then head to the room at the top.
You have no choice but to fight the monsters (beating them turns on the computer), so fight them! Then check the computer, open the chest (Shelter) and go down the hatch.
If you want to avoid fighting, hug the top wall in the first hallway. Then go down through the door, hug the right wall, down through another door, and hug the bottom wall as you head right.
Go through the door, and open the chest to the left (Titan Vest) and right (Hammer Arm). Then check the computer. Fight, then take the path that was blocked by the laser. Take the elevator.
If you want to save, go up, save, then down twice. If not, just go down.
Go left and up, open the chest (Plasma Gun), and check the computer. Enter X A B Y at the tone, then go through the door. Pull the switch, then run down.
Go left, up the ladder, and keep going until you meet the robots. You can't help out Robo while they're clobbering him, so just wait until they stop and attack you!
Use Cyclone on three of the robots at a time, and have Marle heal. Keep HP above 80.