Have a look at a free collection of Mars landscapes by Rispat Momit.
Hi all! Lately I have been working with Sketchfab to create a library of landscapes that you can download for free and start creating your game.
I am also hoping to be part of the new store they are working on.
All the landscape packs include main texture, normal map, AO map, specular map and Obj mesh.
You can get the landscapes for free here.