3.03.1 Blue Mountain.
The city of Bothal was an odd city. Situated between the basin of the mountains, with its districts completely divided by mountainous hills, it was hard for one to travel between the different sectors of the city.
That is, if not for the underground railway system. The Metro they called them, a term directly adopted by the book that Venkatraman wrote before his death. A book that has knowledge of the technological intricacies of modern humanity on the other side. And by deciphering it, the dwarves were able to mimic it to some extent.
When the Technology in their hand was mature enough, they developed their own railway system that ran on electricity and not the old coal trains that would have made the underground inhabitable by all the smoke it might have produced. With a high chance of many of the passengers dying, just like many of the dwarves died during dark days of mining in deep mountains and using up the oxygen in it.