Relief Terrain Pack 3.3 (RTP)

Relief Terrain Pack is a must-have asset for anyone planning to make a game with a terrain in Unity. RTP allows to you create quality terrains that are simply impossible to create with Unity’s terrain editor alone. This asset allows to create advanced terrain geometry such as caves, adds AAA pbr shaders, and provides a myriad of terrain tools even for mesh terrains. I found this tool works best with Unity 5.4.x for the moment, but it’s worth a downgrade and certainly an upgrade to integrate into your project.