Landscape Generators

Let’s be fair, nobody likes or would ever like to have to generally create landscapes. And don’t get me wrong, there are mostlikely some people who do it. I, however, am a civilized person, meaning I am lazy. And so, I would love if could offer me some help, dear veterans of scene creation. Why? For I am a single-man team, and there is no way that I will ever have time to create a detailed landscape before my deadline. So, I come to you, my dear mentors, to ask of our help. What are some landscape generators, and I know there are a few out there, that could generate some textures for Alpha Brushes?

P.S. could you please also describe the specifications for said brushes, because I dropped a few into Unreal from World Machine (they were grayscale and 512x512) and they did not work.