In 1999/2000 I worked on my own Thief levels using the dromed editor - it was both really fun to work with, and utterly frustrating - in a time before open source engines - there were so many small annoying bugs in the editor that would cause it to crash, so you SAVED often and even learned to version files as it was easy to screw up.

But the geometry that could be created was stunning - from courtyards to cathedrals, levels allowed clever use of light and shadow.