title: Walls not showing
body: <p>I exported some mesh in fbx format and imported in Unity. As you can see in the screenshoots, the walls are not shown to the camera. Why is this happening? How can I fix this?</p>
  
  <p><a href="https://i.stack.imgur.com/l3y7D.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/l3y7D.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/ZvAHZ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ZvAHZ.png" alt="enter image description here"></a></p>