"@ the expert@ I don't know anything about sandbox. How doees it works ?"

Just buy the game Far Cry : 10 Euros now !
You have an editor to play with , not complicated to use :
what you see is what you get


That's outstanding ,it is so complete :shaders,terrain,physics editors etc ...
and so complete for an old engine in terms of effects,shaders ...
it is considered old game : more than two years now,
Crysis is arriving ...
And in indie market we don't have (and not before lot of time)
something as complete as far Cry editor/engine

Well let's just prey