What is a bgl file and how do I open a bgl file?
A BGL is a data file used by Microsoft Flight Simulator, a flight simulation game. It contains scenery data for flying locations and airports. Small locations require a single BGL file, while more complex locations and airports may use multiple BGL files. BGL files included with Flight Simulator should not be modified. However, custom BGL files can be created to create custom flying location and airports.
Relevant bgl file links:How to open bgl file on Youtube
How to open bgl file on Wikipedia
How to open bgl file on Microsoft.com