Smoth Fade-Out Material?

Hello Guys!

I have a small problem in the development of my game.
I’m creating a game with a style similar to diablo 3. Would like to know how to make a smooth transition from an opaque material for a completely transparent?

Its something like this video:
When the player enter in the tunnel, the ceiling has a smoth fade-out…

Thanks Guys! :slight_smile: