Terragen is my thing....

Have you ever used WorldMachine? very good terrain program! 

Looks good, did you use WoldMachine to import your lunar terrains into Unity ?

Was it simple enough to export and then import the height map ?

I did not use it for the current terrain I am currently using an extremely low poly mesh (may change to a proper terrain system now its on PC, but people have said its good enough the way it is so why change something if it doesn't need fixing) however I have used it before in personal projects before I started moonbase, I used it in UDK which in my opinion is a bit harder to work with than unity and it was fine in there, from what I have read from the unity documentation on terrains it should be just as easy.

It seems a little harder for cryengine that I have seen but thats because of the issues around that engine rather than WorldMachine.

This guy has done some awesome work with it here is his cryengine work

and this is his set of tutorials on how to use it

But a reminder to all if you have any 3d skills please dont hesitate to post, I got some news to share with you guys!