MISSION 08 - The Secret Of Vis Electra
Prerequisites: Liberate 3 provinces in Insula Fonte
After starting the mission, Dimah will point out a huge set of glowing pipes leading into the mountains. Rico, like the well trained dog he is, needs to follow these to their source. The pipes are pretty easy to follow (due to the glow) using your grapple and parachuting skills except for one that comes up on the far side of a lake from the one you are investigating, so keep your eyes open and you should get to the end of the pipes pretty easily. If you're having problems, just watch the video from 00:46 - 2:28.
When you reach the end of the pipes, you will find soldiers on a gunboat waiting for you. Reel onto the gunboat and shoot the enemies face to face or just rain down RPG fire if you're feeling lazy. Either way, when both of the boats are on the bottom of the lake you'll need to head for where the final pipe ends. Splash down into the water beside the end of the pipe and if you swim below, you'll see a massive gate that Dimah will shortly open for you. Make sure you return to the surface to take a breath before you swim into the huge tunnel beyond as it is an extremely long swim (which I barely made due to watching the gate open) into the facility.
Use the glowing pipes as a guide to get you to the end of the tunnel, emerging into an underground base. Head up the nearby ramp and stock up on ammo at the weapon locker in the left corner before approaching the metal door ahead. Use the gate controls to the left of the metal gate to open up the door to see a massive trio of generators that powers the FOW system for Insula Fonte in front of you. Do what Rico does best and start wrecking shit, exploding all three generators and blasting down the few soldiers in the room.
When the carnage is over, look for a large hole in the wall to your right, this leads back outside to the open air (why we couldn't come in this way is beyond me). As you exit the tunnel, the mission will be over, giving you access to the region's central command facility.