Fortbyte number 23 of the decryption challenge is located near a snow-covered bunker, which means you have to pick it up on the snow-covered island that is completely south of the map.
Warning: don't forget to equip the Jonesy outfit of the bunker which is obtained at level 23 of the season 9 battle pass (paid version) to be able to pick up this Fortbyte.
Written by Augustin "TheGreatReview" Héliot. Translated from French by Millenium.us.org.
The challenges and Fortbyte locations of the Fortnite Season 9 decryption challenge, as well as the complete list of Fortbytes, are to be found in this article.
