The M.A.S. facility in Splendid Valley, home of the Alicorns and our good ol'
This is how I've always seen it, since the outside has never really been described, and even playing Fallout 2 didn't help. So, imagination.
The red flare on top of the facility comes from a library on the internet.
Next stop, Ponyville. Then, Appleloosa. Then...dunno. Any suggestions ?