OK, here is everything you need to know to get this Achievement.
A CP is a communication point. It looks like an orange generator with a red flashing light, a four footed base and a satellite dish that will spin and ping a blue cone of rings into the air when it activates by your touch. The CPs are hidden and some levels have more that one. You can identify a level with an inactive CP by the green ring around its border on the level select screen. When a CP becomes active, it will open a new side mission. This game contains 26 CPs.
Here's a walkthrough.
######## MAIN MISSIONS ########
This mission has 2 CPs. The first one is just to your left as you begin the level. The second one is on a platform that requires the Cyclone Suit. Go to the left part of the map, as you came in, on it's edge, there should be a pit, if you don't see it, move up or down the edge until you do. There will be 2 pits. One will have a Ballista vehicle and 3 crates of rockets, the other will have a door. Go to this pit, get out of your vehicle, walk down the ramp on the side of the pit and go into the door. You are now in a train, pull the train forward and exit the train.
Enter the Ballista. Pick up the Rockets. Go up the ramp and head straight until you see another pit with a double door. Shoot the door with the Ballista and when the doors are blown off the hinges, exit the vehicle, proceed down the ramp, into the pit, through the door, into a secret passage. Guide your shadow up, along the passage and to the Cyclone Suit. Use the Cyclone suit to activate the CP.
If you return to the tunnel where you orignally grabbed the train, not where you parked it, you can follow another secret path to a car in a maze with a scientist in its lowermost corner.
This level has 1 CP. It's to the left of the tracks just a little ways after you spawn in.
There are 2 CPs on this level. The first one is directly to the right of the building straight ahead of you when you spawn. To the left of the area where you spawn, there will be a gigantic parking lot full of RDUs. The CP is on the rights side of them.
There are 2 CPs on this stage. The first one in on a concrete island, between two wooden bridges, clearly visible during the mission. The second CP is inside the Black Castle near the J-Bomb robot.
This level is occupied by 2 CPs. To get the first one, exit the train and run towards the caboose. There will be a CP near the track. For the second, at the first fork in the road, go right, the lower path. Take it around to a grassy area with a concrete jump wall, go up the wall and there will be a trail of RDUs. They will lead to the second CP.
This level has one CP in it. As soon as the level begins, turn around and move the TNT into the stone slab. Beyond the stone slab is an Easter Island Head that needs another TNT. Get aboard the train with the Ramdozer. Take the train to the stain and destroy the Station. It must be done in a particular order. Take out the blue pole nearest the stairs, then the other pole, then hit the double doors of the cafe, after that, ram the right side of the back of the bubble window that remains. After the building is down, there will be a crate of TNT there. Using the Ramdozer, put the TNT on the train and take the train back to the beginning. Park the train so the TNT is right next to the Easter Island Head. Wait for the TNT to explode. This will Expose the Cyclone Suit.
Take the Cyclone Suit. Follow the train tracks to the water. Fly up and follow the cliffside. Soon the cliff will narrow into a bridge and you will see a concrete slab next to the water on the left side of the land bridge. The CP is there. After you get the CP, Go left and follow the cliffside once more, it will curve around and you will see another land bridge, standing on it, you can see another stone slab near water, this one with a Trailer containing a Scientist.
This stage contains two CPs. Go through or fly over the road tunnel to the left and you will see a canal, follow it down to a red explosive vat and some shipping containers. Destroy the vat to reveal the first CP. The next CP is on top of a tall stone pylon just to the lower left of the exit truck. Approach the pylon, stomp the ground, then hold boost for the tallest jump.
There are two CPs on this map. For the first one, head across the water and grab the Cyclone suit, next head out into the water on the left, there should be two islands, one has RDUs, the other has a CP. For the 2nd, head over to the finish the level truck, then follow the road next to it down, it will curve next to a steep rock cliff, on the cliff is a shelf that has a CP on it.
There are two CPs aboard this ship. Turn left up the mountain at the first curve in the ditch from the start area. There will be a space in the rock with a CP and RDUs. For the second, head across the bridge to a secret area with a CP and more RDUs.
This level has one CP. Take the Ballista to the left on the grass ledge all the way around and shoot the buildings on the platform. Go back to the beginning, Shoot any shipping containers that are blocking the Ramdozer. Get out of the ballista, run to the Ramdozer and take it across the bride. Drive left to the platform, get out and run up the ramp to the CP.
This area harbors a single CP. Follow the trench, the CP is under the small stone bridge.
This area is home to 1 CP. If you head to the right, you will encounter a stone wall with a conspicuous slab next to 3 rocket crates. Using a number of rockets, you will bring the wall down revealing a ramp leading to the CP. There is also a trailer here housing a scientist.
######## SIDE MISSIONS ########
Take the road all the way north, there will be a fake wall, drive past it for the CP.
Follow the river all the way to the left as the stage begins and you will find this CP.
The CP here is inside the Black Castle.
This CP is inside the only building in the level.
The CP on this Island is to the "northern" part of the island, there will be a shelf on the mountain with the CP on it.
Fly out of the Volcano to the Lower Right side of the mountain, there will be a grassy area with a CP.
Past the pylons will be a concrete island with a CP on it.
That should be the last of them. Thanks for checking out my guide.