According to B.O.W., this beautiful valley is still a work in progress they started back in January, deciding to experiment with terrain built with Nanite on static meshes. Since then, the accuracy of the terrain "has improved, but it takes more time to test and make".
Currently, the artist is working on improving the water surface, referring to Dai Wei's solution for water disturbance and being satisfied with the results. "I still use a relatively simple method to make the water surface. I did not use Houdini to calculate the water cache. Next is the WPO wind force of the vegetation", commented B.O.W.