I'd liken to see some areas with effects such as echoes where you yell and it repeats back. Some places would echo back more than others.

Another effect would be voices from one area heard plainly in another area unless whispered. The ones speaking have no idea they are being heard.

Creatures that would attack sound such as people talking. Also plate armor would be a give away to the blind cave creatures. I'm picturing great worms that call the cavern home.

Bards would make great bait here.

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