Setting
The author made some accounts on the setting. He did say it was about World War I done differently so that would place all the happenings in 1914-1916 and mostly in Europe.
Austro Hungary
In the part in the book where it described an Austro-Hungarian city, it made me think of the medieval times, sort of. The streets filled with people doing business in the streets, and traveling vendors all over the place.
Great Britain
During the time the Deryn was in London to start and during the Leviathan's short trip there has informed me of the following. London was apparently a boring city with grand buildings and all that. The saw a chapel and other things most cities have. They landed in Regent's Park.
Switzerland
Switzerland in this book, or at least where Alek's Safe House is, is mostly uninhabited. The land is described to be barren of all life. Switzerland is a good hiding place for Alek, but a bad one to crash an animal which needs food to survive and also produce Hydrogen, the element that lifts the Leviathan off the ground. This is where half of the story generally takes place.