What series/book has your favorite world building?

I am reading the second in Mila Vane’s A Gathering of Dragons series. As was true in book one, A Heart of Blood and Ashes, the world building in A Touch of Stone and Snow is amazing.  It got to wondering about other books with great world building. I thought the spy world in Joanna Bourne’s books, the Viking paradise in Larissa Brown’s A Beautiful Wreck, and the post-apocalyptic water soaked world in Megan Crane’s Edge series.

How about you? What book or series has world-building that blows you away?