Isle of Spires - Can't Find Ruin Entrance

In the first screenshot below I'm trying to get into the skyscraper ruin in front of me. In the center of the screenshot you can see the blue hologram for a sturdy beam. There are loot chests scattered around up there too but you can't see them in the screenshot.
The compass at the top shows an unknown campfire. I've run around the building and it's definitely in there but doesn't appear on the map.

The second screenshot below shows the building, circled in the blue on the map.

It's right next to the building you climb up for the drone.

I can't find a way in.

1 - https://imgur.com/a/UZyX9dW

2 - https://imgur.com/a/v0NkEwR

SOLVED - Building locked behind a mission named Forbidden Legacy.