Make two copies of Disk 2 then make up your parties on both disks. Play the game as usual, but when you find any secret passages or walls, or unlock any doors, insert the other disk and continue playing for a short while. This passes all the data onto this disk. Replace the original disk and continue playing and now, if you get stuck in the game and you have to start again, simply continue with the other disk and all the doors that were previously locked will be open. Plus, you'll be able to pick up the keys that you needed to unlock them as a bonus!

The following solution was created by someone other than the person who created the (graphic) maps. Thus, unfortunately, the position numbers used in the solution do not appear on the maps.

Portals 
Level 1 
Level 2 
Level 3 
Level 4 
Level 5 
Level 6 
Level 7 
Level 8 
Level 9 
Level 10
Level 11
Level 12