> Is there a way to use media to make water raining down from the slots
above,
> or do I need to make a raindrop macro and millions of droplets?


Rain is difficult for a few reasons. Each raindrop needs to have a surface
to properly refract light, which means media alone won't produce the correct
result. Even then, in order for that surface to produce the proper light
reflections and refractions, you need to have enough samples on the raindrop
(anti aliasing can help here). On top of all that, for really realistic
rain, you probably need motion blur, too. You can always fake this with a
cylinder instead of a sphere for each drop, but it's hard to make that work
with refraction if you want to make it "transparent" towards the top and
bottom of the cylinder.

You can *try* media with some sort of density pattern to form the separate
rain drops, but I'm not sure how well it will work.

Regarding your image: It's a good image, but the lighting is hurting it IMO.
It looks very uniformly lit, and there are unexpected sharp shadows from the
pipes (I take it there are invisibly light sources floating around
somewhere). I'd like to say that you should rely on radiosity for the
lighting, but there are so few sources of light that that would probably be
very slow and cause artifacts. So here's what I recommend:

 - Make the sun and sky much brighter. If we're in a dark tunnel, our eyes
would be adjusted to the dark and the sky wouldn't look grey like it does.
Both the sky and the light hitting the floor would be very bright, so I
recommend bringing that up.
 - Make sure to use a very low ambient value; you can't rely on ambient when
your entire scene is lit by ambient light. You'll have to fake the ambient
lighting on your own:
 - The three main sources of light in this scene are the opening in the far
back, the slits on top, and the light bouncing off the floor from where it
hits on bottom. In each of those places (the door in back, the three
openings on top, the three places light falls on the floor and maybe some
more places off screen), create a large area_light that covers the source.
You may have to use light_groups to make sure that, for instance, the area
lights near the floor don't light up the floor. (Another possibility is to
give the floor no_shadow and put the area light underneath it.) Use a lot of
samples for the area lights, since the point is to get very soft lighting.
This may be slow, but it will probably be faster than relying on radiosity
alone. Also be sure to turn off media interaction with these area lights.
 - Finally, you might try adding radiosity on top of all this to increase
realism and get more variations between well-lit and poorly-lit areas.

You do seem to have a good handle on the media!

 - Slime
 [ http://www.slimeland.com/ ]

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