There is only one file type that uses the .LMU extension:
RPG Maker Map File
Map for a role-playing game (RPG) created with RPG Maker 2000, 2003, or XP; includes map layout, different types of terrain, and objects such as trees, plants, and rocks; usually based of a theme such as a forest, mountain, cave, etc.
|Enterbrain RPG Maker|
Updated: September 21, 2007