you didn't make this map.
https://www.ugx-mods.com/forum/map-releases/29/octagonal-ascension-challenge-map-1-3-update-its-impossible-now/10765/
 
 

try downloading nazi zombie dessert or something like that its a huge box map and lots of room to train, the boss comes later in the stage and if you have good weapons then you will have no trouble trying to beat the boss

how do i get this to work on solo???