Outer Heaven

From the Encyclopedia of Speculative Fiction - http://encyclopedia.wizards.pro

Outer Heaven is a gigantic, impenitrable fortress 200km north of Galzburg, South Africa. It was founded by a legendary soldier, and is the location where the first Metal Gear is being built.

Spoiler warning: Plot or ending details follow.

The legendary soldier who built Outer Heaven turns out to be FOXHOUND commander Big Boss.