I'm about to run Stonegarden soon-ish. I expect the first one or even two sessions to take place overground with players exploring the city part and getting familiar with the dwarves and they could use a few days of respite right now . But I'm also preparing for them to delve into the depths and here I encountered this thing with the "thick air", which lets the dwelvers speak only once at least 200m below the surface. Physically, that is total nonsense, isn't it? I mean, mines nowadays go deep down and air pressure does change with altitude and it impedes your breathing - but not even close to explain this hearing and speaking issue of the dwelvers. (It would basically mean that humans cannot speak when visiting Peru or other high altitude locations.)
So right now I'm not sure if I will just throw out the whole "they cannot speak above ground" or explain it some other way, like a vow they took or just spite / mischief, because they seem to have a low opinion of their surface dwelling descendants anyway.
What did you do with this and how did your group(s) take it? I'd like to collect some ideas here. Thanks .