skynet you are not alone probably, i just figured out last year when i opened it in Unreal editor because i wanted to try to make a winter version.
This is what it looks like in the UT99 editor.
UT99 works with subtractive system and the new Epic engines use additive so i need to use a different approach.
i use intersect with a giant brush around the whole map, exported it as obj and then used it as reference in Maya to make new static meshes with the exact same size/ratio and then exported them as .fbx file in UEFN / Unreal Editor for Fortnite,
i only need to UV map and texture it and add a flagroom and floor and ceiling.