Holes in walls when importing to Unity

I have modeled a house for my map in Blender, and then imported it to Unity. The outside looks fine, but on the inside some of the walls and other platforms are invisible.

Here is the outside:

Here is the inside:

See that giant gaping hole where a wall should be? Anyone know how to fix this?

Were your face normals correct in blender before you exported it ?
Turn on normal display in properties panel (shortcut N) when in edit mode.
You can flip the normals of selected faces with W / Flip Normals

Okay, I’ll try that and tell you how it goes. To expand my knowledge, what exactly are normals?

The normal of a face is basically telling the direction to which your face is pointing.

When you are in Solid display by default you don’t see when anything is wrong because in Solid mode both side of a face are drawn and lighted.

Now you press N , scroll down to “Display” and enable “Backface culling” and then you’ll see immediately if one of your normal is wrong as it will look as if that face is invisible (due to the normal pointing in the wrong direction, leading the engine to think it’s a backface).

Usually when you look at your model and see some very odd darker faces, it’s usually a good hint too that you have wrong normals for them.

Thanks for the help guys. It worked perfectly.