Fortnite

This is story-related and can't be missed.

When you complete the first stage (Stonewood) you unlock a second stage, called Plankerton. Your first story-related mission there will be a Storm Shield Defense quest. After completing that, you will have to complete a quest called Two Sirls, which is the quest you need to complete to unlock this achievement.

For the quest itself, you'll need to complete a dual-storm quest in a 19+ area. These dual-storm quests are quests where you have to defend not one, but two atlases at the same time. This can be very tricky if the atlases are far away from each other, so my advice would be to keep searching for a lobby until you find two that are close together. That way, you can build one big fort and defend both pretty easily.

As usual, the achievement will unlock when you open the envelope with your rewards in the rewards screen at the end of the quest.

So, in a nutshell:

1) Unlock Plankerton
2) Complete Plankerton SSD 1 to unlock Two Swirls
3) Complete Two Swirls
a) Join a dual-storm match
b) Explore the map to find both atlases
c) If they are close to each other, go ahead
d) If they are far apart and hard to protect at the same time, quit the match and go back to a)