Serious Sam Revolution - Military Decay 1 (Serious) 

Here's a a three-levels campaign set in some kind of military buildings in the middle of nowhere. This first level is almost entirely set in outdoors environments, works good as introduction to the campaign. Thanks to the creator Unwary_Thief and to Mydlak for republishing it and adding some stuff
Steam's workshop page:
steamcommunity...
I've played this map in blind run at Serious difficulty. When you see the fades, it generally means that I've died there, or that I went back somewhere to pick up some stuff or that I've reloaded 'cause I let myself be hit too much in stupid ways