Finding one of several Boomboxes will help you finish a Legendary quest in Fortnite Chapter 2 Season 7.
There are four total to find - double what you need - with this page explaining three of the locations to give you some options.
This challenge is also a useful way to get abducted by the mothership - which tends to happen more often than not in the Believer Beach area.
Boombox locations in Believer Beach explained
You can find Boombox locations in various locations in Believer Beach. Here are three of the four positions we found - one more than enough to complete this challenge:
We'd recommend going to the one to the south-west, by the bus on the road. This seemed to be the quietest, and means you are then close to one more to get this challenge completed quickly.
Another is on the main strip, west of the main pier, where the V and E of Believer in the mini-map meet. You can find it next to some equipment surrounding a table.
One more can be found in the north-west, on the beach. Specifically, look out for the large alien pattern in the sand where Sunny is located, and next to the parasol so the south-east will be the boombox location.
Once you have placed two boomboxes, the challenge is complete - next up is alien communication devices on mountain tops.