FatsXL wrote: Maybe a new unit could be created that "burrows", switching between under and above ground terrain at any location for a modest movement cost.
That's exactly what the Sandworm is.
Dungeon/Underground terrain would be much better if the entire map had to be dungeon/underground. That is, no above ground at all. So that someone could create the Mines of Moria as a map. Some existing map stuff like volcanic and all the water terrain can be used 'as is'. So can roads, ruins, sites, temples and all the walls/arches , cities etc. We'd just need some cavern floors, cavern walls etc.
KGB