These fog and sky effects are together called from Light.dbc. They are commonly called skyboxes, while skybox is just a part of whole system, so its a little bit incorrect.
Check Light.dbc and simply delete sky systems which are located in Nagrad. Just beware, both XYZ coordinates and 2 sizes are not in yds nor in game coords.:
pos.x = 17066.666 - pos.x / 36.0f;
pos.y = 17066.666 - pos.y / 36.0f;
pos.z = pos.z / 36.0f;
falloffStart = falloffStart / 36.0f;
falloffEnd = falloffEnd / 36.0f;