Barriers are the colored walls that block off passage ways and certain treasure chests. They come in 5 different colors: Blue, Red, Green, White, Black. To open the barrier you must have the device for that certain color, the devices can be found at these places:
1. Blue - You will get this as you are leaving the robot town of Baroy.
2. Red - By defeating the damage Defense Mecha Robo in the Ancient Factory.
3. Green - This will be given to you after you disable the green barrier around Pachess Town
4. White - Obtained after defeating the Iron Giant in Noluta.
5. Black - Obtained after killing the Azure Dragon boss at the end of the Sea Cube
Check out this link for a full list of the barrier locations:http://www.xbox360achievements.org/forum/showthread.php?t=37...
Note: If you talk to the fortune teller in the Lai Mountains Sheep Camp she will tell you how many of each color barrier you have remaining, the catch is she only tells you of CHESTS with barriers not passage ways. So if you talk to her and she tells you you got them all and you still don't have the achievement, then that means you are missing one blocking a passage way.