I took the liberty to include a skybox with the level since it fits with the theme
(dayblue city). The name of the author is unknown but thanks to him and thanks to 
Fakir for including the skybox with his level FBSP003 (that's where I got it from).

To install it simply create a folder called 'Sky' in your Duke3D dir and move the 
six included JPG files into it. Then copy 'Duke3d.defDELETE' file to your Duke3D 
dir - AND rename it to Duke3d.def (just remove the 'delete' part). Or if you don't
wish to overwrite your previous duke3d.def then just open the new one with the skybox
tag, copy the text and paste it in your own duke3d.def.

The skybox won't work without Jonof's port. 
-http://jonof.edgenetwork.org/index.php?p=jfduke3d

-Mikko Sandt
http://www.planetduke.com/msdn/