I was thinking there might be a guest room for humans down in Atlantis. But this raises a question: how would they get enough oxygen for their guests?
Mines have various techniques for oxygenating themselves, including the use of fire, and horse-powered fans (sometimes the two together). So perhaps this could draw air down through a sort of chimney? That chimney would have to be pretty tall, though, and that would risk leaks or other damage.
It would be possible to collect air in water-proof containers, then pull it down to the city, then release the air. That would be quite a lot of work, but it's at least simple.
Does anyone have better ideas for how to keep landlubber envoys from suffocating?