Porto Cavo

"The sprawling Porto Cavo naval base is the main dispatch of marine units across Medici's island chains. Its use of existing cave features offers a measure of protection from both aerial assault and surveillance, forcing would-be invaders to navigate the narrow, heavily-fortified waterway."

Porto Cavo is a military port in Just Cause 3.

Description
It's a large military base, consisting of two parts: An above-ground area with an airport and a harbor built into the caves below. The above ground area has mostly communications equipment and the underground part of the base is home to many fuel tanks and Distillation towers.