Worst-case scenario: the UEd Goblin wipes the map and burns down your house.

From Unreal Wiki, The Unreal Engine Documentation Site

A Map file is just like any other Unreal Engine file packages. Being a package they can contain all types of resources; the .unr file extension is merely a convention to denote "this package contains brushes and actors that make a playable map."

Check Antonio Cordero's website for a pretty thorough documentation of the Unreal package format and a Delphi unit that implements it.

[edit] Related Topics

• Unreal Engine
• File Format
• Package
• Package File Format
• Package Extension Catalog