Ubisoft has released a map editor for XIII, allowing you to create your own levels/maps for this recent cel-shaded FPS. If you have already created some maps for Unreal, you shouldn't have any problem with this one.
Gamer's Hell Local Download:
XIII Map Editor
Unzip the files in the directory of your choice - but NOT in the game directory.
To start the editor, go in the sub-folder /System and launch XIIIEd.exe