Cross over the cell bars, find a new maze, make the maze from it's path, find the cell bars, cross over the bars, find a maze, make the maze from its path, eat the food, eat the path.
I just noticed that back in January Bungie released the Marathon Trilogy for free (beer). Previously they had released the Marathon 2/Infinity engine for free (freedom) and it has since been developed for modern systems under the name Aleph One. But the maps for Marathon were not available for download. You had to own a copy of the game. Since it was released in the mid 90s its a wee bit hard to find. As its no longer available for sale Bungie decided to just give it away. You want to download the complete "A1/SDL files" and then drop a copy of the Aleph One application into the resulting directory to get it going. For Marathon 1 use the M1A1 conversion.
For those who never played this game, and you probably haven't unless you were a Mac gamer in the mid 90s (a woe be unto you for that), its a contemporary of Doom yet far suprior in graphics, level design, gameplay and story. Its a 3D shooter instead of the 2D (with a 3rd faked) of Doom. The engine still holds up well, but its nothing compared to, say, Quake 3. The engine isn't the point. The point is the story.