They are a button on the top near the Collision planes.

I don't think putting them in mountains would do much. You have to calculate occlusion like I said earlier. Then it doesn't render anything behind the mountains at all.

That would probably be the silliest thing you could possible do. LOD does this by fading out the objects not within a loaded cell, and replacing them with lower quality meshes when applicable. Slapping a whole mountain in an occlusion box would do... basically nothing.

I do not mean custom mountain models with oclusion panels inside , Imeant stuck occlusion boxes in the CK where is landscape higher grounds and mountain objects ....