Using Commune With Nature underground should trigger a quest from an underground questgiver.
I know getting quests from underground questgivers happens during quarryman/miner/cave hermit "greet/consult" quests with them, but after that you can't get them anymore. I like exploring underground endlessly already, so this is like one place where I would like some quests!
Furthermore, quests from underground questgivers should be underground themed, similar to those quests seen during miner and especially cave hermit. Mine X on level Y. Deliver stone/ore X to underground questgiver Y. Pick an underground foragable. Defeat a bat/slime/worm/troll. Visit (NOT EXPERIENCE) localized resource X. Stuff like that, and the usual questing stuff.