How Can I make Tunnel In unity?

Unity Engine
1

Hey’ So I was trying to make Tunnel and this happened It looks invisible from inside


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I use blender first but did the same and I used Pro Builder too

I started with a cube and deleted that start and end face of the cube.

Yeah! It looks invisible from inside what should I do I’m newbie

So, how Can I make Tunnel In unity?

5100194--502802--1 (1).png
5100194--502802--1 (1).png1366×685 141 KB

5100194--502805--1 (2).png
5100194--502805--1 (2).png1366×685 146 KB

2

Duplcate faces in blender and flip normals for duplicated.
Or disable backface culling on your material.