Quote from King Of Sandvich on December 26, 2010, 6:15 pm

What I was trying to say is that while you could theoretically do this with props and other game elements, you simply cannot tamper with the structure of the map itself and expect to get a good result. It's hard enough to make a pop-out wall in hammer that has good lighting, much less adjustable sections of the map itself. source is just not designed to have brush entities make up the map itself. Visibility and lighting are designed to be pre-calculated, so that other things can run so smoothly. Trying to create a good looking section of the map ingame just doesn't work.