Crackdown 2

The final act of the campaign - so if you're completing the campaign, you'll get this achievement right at the end!

Once all the beacons are activated, you'll have a couple of small tasks to clear up - basically head into the refinery and start up a few of the pipelines to allow power to flow back to the Agency tower...

Head back to the tower and climb up to where the first set of interweaving walkways start. Some fairly heavy duty freaks will start climbing up and attacking the tower component of the Sunburst beacons. Much like the beacons you've already defended, just keep blasting away at all the freaks that come into view until tower beacon is charged. Unlike the other beacons, this is done as a three-part section, so you'll have to guard three separate sections of the tower (just keep working your way up the various sets of interweaving walkways.)

Did this in co-op, and to be honest, it was a fairly close thing with the last section (close enough that we weren't sure for a few seconds if we'd succeeded or failed!) but again, I was using the HMG gun to try and up my weapon stats, where I should probably have had a couple of rocket launchers armed.

When you've successfully defended the last section, it'll flip to a cutscene, and the chievo will pop...

Finish the final mission. It does not have to be your game. I helped a friend finish the game and I have a ways to go and missed a good chunk in the middle of the game and still got the achievement.

The final mission unlocks when you have detonated all 9 Beacons. You do not have to do strongholds, or breaches to unlock it.