I can't imagine modular mountains are possible, at least not the way this course teaches. I think you'd have to model a few mountains and duplicate them around to generate the larger mountain range. This course would be very relevant.
The only modularity to the tower I would consider is to control the height. So imagine you have the base segment with the door (call it piece A) and the top with the chess rook pattern (piece C). Then you could create a middle segment that's tileable (piece B) to control how tall the overall tower is. The options would be like this:
C C C
B B B
A B B
A B
B
B
A
