Stage: Schwarz Wald
At the end of this stage-- set in Germany's Black Forest-- the player comes upon the giant Le-Ostro fortress among the trees. Only a small portion of the fortress can be seen. Le-Ostro fires projectiles from its turrets and roofs; when it takes enough damage, its facade falls away, revealing an underground base similar to Holly Mountain. Le-Ostro does not appear to be a real-life structure.
Le-Ostro returns, now completely visible, in Assault. The mission to destroy Le-Ostro is timed, which along with the boss's location, makes it difficult to destroy. As the fortress is nestled in the mountains with a force field protecting either side, it is best approached by diving down, firing a few shots, then pulling up again quickly. However, this can cause the player to fly straight into a mountain, a force field, or Le-Ostro itself.