Rendering part of the mesh

Hi!

I wonder how to render complex mesh (my own terrain-like mesh) if I need to render only part of it visible from defined place (not always visible from the camera). Think for example of the case when there is a part of the terrain which obscures view (eg mountain) to the car driving in valley. Now my camera is in isometric far view but I still want to render visible mesh first and then rest only if it doesn't obscure my first pass. I thought about distance test but it isn't effective in complex caves. I think I need to ray cast test visibility of the triangles and then sort them to be rendered in my first pass but I'm not sure how to do this. Any help would be great. Thanks.