I would wish we can create underground dungeon map which link to existing map.
a) Dungeon gate are the link between existing map and underground dungeon map
b) There is limit entry of dungeon gate where large unit do not able to enter or exit(eg. Kraken , mammoth, green dragon, devil , great archon , red dragon)
c) This can be solve by expand the dungeon gate using units that have construct skill point. Expansion of dungeon gate required 150 construct skill point. Suggested construct skill point for units;
Light Infantry 2 construct skill points
Heavy Infantry 2 construct skill points
Pikeman 2 construct skill points
Dwarf 3 construct skill points
Giant 5 construct skill points
d) Underground dungeon provide treasure room , underground mine , underground city and a passage between continents (apart by sea) in existing map.