So you can fly. [Ships, she is familiar with. Airships, not so much, but she gets the general idea. Flying ships.] That is something we do not readily have in our world. Neither do we have transport underground, beneath a city. I suppose the only similar thing would be the abandoned mine shafts, and the carts inside them, though I would assume it would be much larger and safer if it was used to carry humans.

If it goes beneath the entire city, it must be quite useful.