A complete scene and prefabs created in unity. allow you to get you started rapidly.

Mountains, ruins and cave areas are all included:

http://u3d.as/1ypw 

The cliffs/rocks and ruins feature a trilanar shader, you can customize the colors/textures and overlays. The water and vegetation shader are also customisable. 
The trees/vegetation prefabs are using unity's terrain system and are already set-up for you. The ruins prefabs are modular and fit on a grid. 
The cloths prefabs are using unity cloth's system and can be adjusted. 
Particle effects, air particles, clouds, mist , butterflies, etc...

Trailer: