Importing a double sided plane

I work on Blender a lot to make my models, and in this case I made an island and I am importing it to Unity 3d. When I import it, it is one sided like a plane, and I can only see the inside of the island instead of the outside. Is there any way to fix this problem? Any answers would be greatly appreciated.

The easiest solution would be to use a custom shader. The reason blender is showing both sides is because the shader it uses to display faces sets Cull Off, which draws faces no matter what direction, while the default unity shaders use Cull Back, which only draws faces facing the viewer (improving performance). For instance here is a two sided vertex lit shader

Shader "Custom/Two Sided Vertex Lit " {	
	Properties {
		_Color ("Color", Color) = (1,1,1)
	SubShader {
		Lighting On
		Material {
			Ambient [_Color]
			Diffuse [_Color]
		Pass {
			Cull Off