The Odyssey is a nostos, the story of a hero's return. To get home, Odysseus must journey through the underworld. That particular journey is called the nekyia, and is a key element in the structure of an epic.
As we began to discuss and query in class: just where is home for Odysseus? Where is the Ithaca of Homer's Odyssey. Here are a few resources on that question, including some maps to supplement those included in your book.
Ithaca, generally: https://en.wikipedia.org/wiki/Ithaca
Homer's Ithaca: https://en.wikipedia.org/wiki/Homer%27s_Ithaca
Geography of the Odyssey: https://en.wikipedia.org/wiki/Geography_of_the_Odyssey
A wealth of links on the geography, as surmised from the 12th Century to 2010: http://homes.chass.utoronto.ca/~jburgess/rop/pages/bibliography.html
The mystery continued at Odysseus Unbound: http://www.odysseus-unbound.org/
My personal favorite: The Authoress of the Odyssey, Samuel Butler's theory: http://www.joh.cam.ac.uk/authoress-odyssey-1897
An interactive map: http://www.classics.upenn.edu/myth/php/homer/index.php?page=odymap