For whoever with the skills that I lack (it may be a quest or new area):
[INDENT]... somewhere in the Underdark, there is a exuberant valley filled by the Underdark version of surface cicadas. Their constant noise has a sleeping effect upon whoever listening to it, so, crossing this valley is a hard and, for several, impossible task. Tales of travelers falling asleep in the valley and never awakening again are a constant in the few settlements around it. Still, some brave (and maybe stupid) adventurers insist in crossing this valley due to rumors of treasures hidden beyond.[/INDENT]
why
There is no means in which to accurately represent the beauty of the cicada and its harrowing song. The most anyone could do is the generic swarm monster which is overdone as is. I'm afraid we might never be so blessed as to have an entire quest dedicated to the Seven Year Locust :C.