Ok, so, mucking around a bit more I've learnt that F4 on the keyboard is the default "show all" button. This allows me to fully view interior instances and potentially make maps from them as I would exteriors . . . however, it also shows spawn points, light sources, audio nodules, pathing waypoints, and other things which disrupt the "purity" of the map.
Does anyone know of a happy "middle ground" solution, where I can see the map geometry without also seeing the "invisible" data points?
Thanks in advance!