I built a very very simple building out of 4 planes in Blender. A “roof” and three sides. When I put it in Unity and play the game, it only renders the “roof”, as I walk closer to the walls it eventually renders them. Most of the time it only renders the walls when I’m actually in the ‘building.’ Never rendering more than two walls at a time, though. What gives?
Probably a normals issue. Polygons are normally noot visible from behind, except when you use a two-sided shader (i.e. culling off).