Gaia is great for environments,
Unity Plugins
Generating terrain is one of the most common requirements for any 3D game. Doing this from scratch takes up a ton of time, which could be better spent on other areas of game development. Don’t get me wrong, terrains are vital to any game’s success, but if you can make use of an off-the-shelf tool to do all the heavy lifting for you, then why not? That’s where Gaia Pro comes in.
With this one plugin, it becomes possible to generate entire scenes in only a matter of minutes. You start out by creating mountains, hills, mesas, lakes and rivers with a few simple clicks, and then spawn a biome for texturing, planting and populating the world procedurally. Finally you set up the lighting, wind, water and a player controller, before pressing play and exploring the world you’ve created.