Floods the crater, drowning all inhabitants and defenders. Drains it, builds up a small island in the middle, and fills the hole around it with lava. Builds a large tower on the center island and reinforces it with corrugated titanium. Places sentry towers equipped with Class-II Hydrolite Mazer anti-personnel on the outer rim. Equips the inner fortress with Class-VI Funkheizer Gladiator cannons, Golan Eagle-III anti-air systems, and a complex sensor system.
Installs a planetary-class blast-absorbing localized shield as an afterthought.
MY. FREAKING. HILL/CRATER.