I'd like to have areas that look like caves, but the tile-set and skybox can mess with that illusion on a tile-set designed for open terrain.
The issue is the global lighting that that casts shadows inside the cave making it look like there is no ceiling.
For maps where the player can free-look, the sky-box could be an issue as well.

For custom cameras: aside from the angles / field of view / target / etc. can they ignore light source settings, perhaps through triggers? (and maybe change sky box per camera)?
Would be nice to create a deep cave ambiance using tricks like this.

If camera tricks are not possible, perhaps I could modify the "xxx_nomal.dds" terrain texture so that it would reflect light differently and appear more like an indoor terrain?

But probably the best / easiest way is to just use extra high raised terrain around the cave area which will cast a shadow and make that area look dark everywhere.

Any suggestions?
( I'll do some tests and put up screen shots )

You can change the light settings for the map to reduce them entirely or place the sun under the ground and cast no shadows I believe.

That would work, but sadly it's a global setting... it would effect all players even if they are out of the cave.
It's too bad lighting is limited to the Terrain Texture Set and not also applicable to individual cameras.

Ah, you wanted per-player lighting. Yeah, I don't really know about that. Editing the normal maps won't effect the shadows, just the way the normal lighting works on textures (shadows are different, since they are dynamic based on meshes).

If you have a falloff the skybox vanishes from my tests back in early release, not sure if they fixed that.

The Falloff should work for background ( I guess shadows too )
I had that happen today and didn't realize it was happening. Was changing the map backgrounds and I could not see them in game because I was applying a camera via triggers at the start of the map and forgot about it... drove me nuts for hours.