I hand-draw all the backgrounds in my comic, excluding the scenes where I traced or referenced 3D models of ancient Roman establishments (from Sketch Up). Background drawing is my vice. I have really simple character designs and really complex, detailed backgrounds. I just really love detail!
There have been times when I attempted to make something in Sketch Up or another 3D app, but it never came out how I wanted it to, and I find my own drafting and perspective skills are capable of producing the scene I want.
Some of my favorite background-designed-by-me pages:
The kids' reading room from chapter 5. Not only did I draw it, I decided to give the picture books consistent covers.
The Dungeon in chapter 6. There was really only one search result for "ancient Roman jail cell" so I based this drawing on that location, with some extrapolation as the pictures didn't offer a 360 view XD
The stables in chapter 7. Mmm, I love slanted lines!
The secret study in chapter 9. Spent a whole week on this page. Was it worth it??? No XD