to interact with, fly over, trenches, towers, bridges, cities

Trenches in what? Towers on what? Bridges to what? Cities where?

A little more description would be a good thing...

you mean, more roids/station thingies like the one in dau?

it'll take a lot of work and time to create anything of the sort :)... but maybe someone who has the skills (or plans on getting the skills) can start sketching ideas, and make models that they can show the devs--see celebrim's idea for planet design.

micki001: explore a little, you may be pleasantly surprised at what you find.