This season 7 week 3 legendary quest requires you to place 3 alien light communication devices on mountain tops.

There are 4 locations where you can do this. At each location you will find a blue outline you can interact with.

The first location is on top of of the mountain next to Apres Ski. The second is at the top of Mount F8. TThe third is just north of the Weather Station at the base of Mount Kay. Thee fourth is just north of Base Camp Hotel.

The locations are marked on the map below.

You should be able to get this quest in one game because of how the alien light communication devices are distributed. There are two close together.

Map credit to fortnite.gg