How To Achieve A Curvature At Horizon.

How do i achieve a real world like curvature when the player sees horizon, is there any asset which can help me do this quickly, or a custom shader needs to be applied( i dont know how to create a shader).

and also, is this a huge performance hit?

Do you mean the terain to make the world round? Then you have to shape your terain that way, or if you use a mesh for that bend your mesh.

You can also achieve this in a shader. Example at: