Water Tunnels

This architectual add on has become a staple
of the shooter genre. They can be used as a secret
back entrance or simply as an obstacle to overcome.

The tunnel in this section is fairly simple for time sake.
You'll need a room of  course with an idea of where the
tunnel will begin and end.  I've just used a basic room to
keep it simple.  The first step will be to cut out the holes
that will be the entrance and the exit.  Make a brush that
will be the same size of the entrance of your tunnel and
line it up with the floor so that the it rests just above and
below  the  floor  level.   Now  hit  the  csg  subtract  button 
and back space leaving a hole in the floor.  Now cut out
the hole for the exit.  Go under the map and create a brush


   

that  will  match  the  opening  in  the floor and drag it 
down below the floor.   Now  make  a  matching  set  on
the  other  side  like  the  picture  below.   Connect  the
two with a brush that has the same height and width.
Go  ahead  and texture all three brushes to  make the
next step easier.  Now hollow out all three brushes by
using  the  hollow tab.  Go  back  up  to  your room  and
remove the brushes that plug up the holes.  

   
Then go down into your new tunnel and move the two
 brushes blocking  the  center  section  up  to  what will
  be  the the ceiling of the center section.  Then remove
 the  end  brushes  that  make  up  the  center section so
  that there is a clear shot all the way through the tunnel.

   

Now it's time to add water!