Sewers
Sewers are quite
easy to put together and can be explained fairly quickly.
Basic knowledge of the clip tool is needed here
First thing to do is to get 4 blocks down to represent your basic sewer,
like so:


Once you
get this far the next thing to do is to add four smaller blocks into each
corner then CLIP them to produce angles.


So now you have your very basic looking sewer, obviously with some decent
texturing and lighting it will look sweeter.
How to make it go round corners? Very easy actually, all you need to do is
copy what you have so far and rotate to form a 90 degree turn and then clip it
diagonally across at the join, let these pics explain.

Here we have the sewer at 90 degrees, its important that it overlaps perfectly
like the above picture.

Then we simply clip away like the above, and also do that to the other side.

There we go, as simple as that. Have a look at cs_siege and militia to get an
idea of how the sewers should look.
By Blink