[Twan]

Iirc only when storming (which is logical considering cave forts can be built out of cave provinces) but not sure.

About maps with caves, I prefer fantasy worlds with an underworld so an high number of caves, and it's why I hope such maps (like the two I've made World of Geometry and Oeridia, but I hope other mapmakers will make some) won't end with big balance issues (I also like fantasy worlds where humans know how to carry a torch, and all serious mages learn the cantrip light spell).

Anyway, if a #darkvision command is simply added for modders (iirc already announced in a thread someone asked for) or even with some copystats (but there are some issues with the units actually having darkvision always having unwanted other stats) -or better a darkvision effect for buff spells / battle enchant (not announced but why not)- I think there will be no problem to make a mod to balance maps even with a huge number of (dark) caves if people want to - it would just reduce a little the power of darkness spell (or let some nations suffer in full dark if people prefer). So I won't argue more over this (eventual) issue.