I've been working on quadspinner Gaea for a while. After learning the program, making the landscape becomes quite simple, the landscapes you see were made around 1 and 2 hours on average. With the landscapes I made in Gaea, I will continue to design environmental projects in Unreal Engine. It greatly improves the environment quality in Unreal.
I've done some minor touches with zBrush in some landscapes, throwing and editing the landscape you made in Gaea into zBrush is pretty simple, I recommend.
Rendered with Marmoset Toolbag.