Strata by Terry Pratchett

It's hard to surprise or shock a person when they've lived more than 200 years; they've really seen and heard it all. But Kin Arad is intrigued by the invisible man who appears suddenly in her office and his news of a flat planet's existence.

This was one of Pratchett's earliest books, and he's setting up the cosmology that his later Discworld books are built upon. It's captivating and imaginative. But also a challenge.

This book moves very quickly and presents some extremely foreign concepts: So much so, in fact, that I concurrently read a paper copy of the book (in the house) and listened to the audiobook (in the car). I have never used this dual approach before, and I found I really enjoyed it. With the audio I got characterization and pronunciation while the book allowed me to take a moment sometimes to reabsorb and wrap my head around a new and complex philosophy.