I'd like to make or download a terrain that launches me at altitude (15k or more), near an enemy base,  to practice base attack.
Can you recommend a download site that may have something like this already?
I've looked at the Terrain Editor application.  That looks way over my head, but, if necessary, I'll give it a go.  Any more detailed instructions anywhere?  
For example, could I just modify an existing terrain by adding a high alt launch?  But I can't even open an existing terrain in Editor.  Sigh.
HONK!
Gooss