this idea over at Underworld Kingdoms for building megadungeon maps by overlaying a whole bunch of building plans — castles and so forth.
This is the sort of thing that computers and the internet have made trivially easy. It could have been done back in Ye Olden Tymes with overlay cels and what-not, but it would definitely NOT have been easy or straightforward.
This sort of layout looks a lot more like real building than most megadungeon mapping. Structures that accrete over ages don't tend to have any overarching design, and they don't generally conform to a convenient grid, having been tacked on to and built over existing construction.
This would probably drive any obsessively accurate mappers up the wall. Muahahahahahahaaaaa!!!!!