Steps of building terrain by the Unity Terrain Editor:
1. Start
1. Start
GameObject> 3D Object> Terrain
Hierarchy> Terrain
Inspector> Terrain> Raise/Lower Terrain
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Use the selected brush to raise terrain in the scene view.
Inspector> Terrain> Paint Height
Inspector> Terrain> Settings> Height> 20
Brush inner lower area.
Inspector > Terrain> Settings> Height> 50
Brush outer higher area.