This Fortbyte can be found at the top of a mountain in the Snowy Biome! Although to unlock it, you must first destroy the gnome that contains it with the Vox Pickax.
The Vox pickaxe is the reward for reaching level 55 of the pass. Without this option you cannot complete the conditions for the challenge.
The Mountain is located in the southern part of the map. It is in Snowy Biome, west of Fatal Fields and east of Happy Hamlet.
The Fortbyte is located at the top of a mountain. There will be an advanced expedition north of your general location.
At the top of the mountain there is a toilet with a lamppost, a garbage can and a gnome on the side. The Fortbyte will be at the Gnome.