While everyone already showed some pics or sketches form his/her works, I might also give you a little impression:

The first 4 pics are from an early, rough city level with A7 which I worked for some weeks but never finished (due to lack of time). Most of the buildings can be entered (all factories and a white house).

http://s221.photobucket.com/albums/dd309/Silencium17/?action=view&current=City.jpg
http://s221.photobucket.com/albums/dd309/Silencium17/?action=view&current=Church1.jpg
http://s221.photobucket.com/albums/dd309/Silencium17/?action=view&current=Factory1.jpg
http://s221.photobucket.com/albums/dd309/Silencium17/?action=view&current=Factory2.jpg

I also designed some levels for "Thief2" (and I'm currently working on one)

http://s221.photobucket.com/albums/dd309...01018_09_52.jpg
http://s221.photobucket.com/albums/dd309/Silencium17/?action=view&current=3-2.jpg
http://s221.photobucket.com/albums/dd309/Silencium17/?action=view&current=4-1.jpg
http://i221.photobucket.com/albums/dd309/Silencium17/1-4.jpg

EDIT: And I also think that Ganderoleg should be the lead-artist.