Construction began in 1657 on what was to become Spain’s greatest and most impregnable fortress they ever constructed in its colonies. In 1762, enlargements and upgrades were made that resulted in the unconquered fort we see today. The fort is criss-crossed by dozens of tunnels that aided in the movement of provisions, man-power, and communication when under attack. It’s not until you are walking within the walls and tunnels that you realize how dauntingly impossible it must have been for enemy invaders. Thankfully we just have to enjoy the view, not worry about cannon fire.