Umberto Eco's Island of the Day Before is probably a book you should only read if you've got prior experience reading exploration literature such as Herman Melville or Robinson Crusoe, and it certainly helps to have a strong interest in philosophy, because Eco ends up spending most of his time exploring the deeper implications of Roberto de la Griva's experiences. It's not a story (or from an author) you will just be able to pick up, but is definitely worth the challenge. It ends up feeling like a time-stamp on the era of exploration, its beliefs, reasoning process, and acknowledgment that Eco believes even archaic ways are worth examining, can still be seen as fascinating.
I've heard from several friends that Eco is someone who seems to be more challenging than the average writer, and in truth, I hit a wall when reading this one, but muscled past it, since the story continually transformed to envelope new ways of understanding what the story's goals ultimately are. There's a whole subplot, for instance, involving a figment of Roberto's imagination, an evil twin named Ferrante who seems to fulfill many of Roberto's personal objectives, including a grand romance that serves as part of the method for which his story is relayed to the reader, through a narrator who is translating and condensing a journal that has been discovered from 1643, possibly by Captain Bligh.
I had originally believed that Island of the Day Before may in fact be an undiscovered antecedent to the TV series Lost, a modern-day version of the exploration narrative also found in The Odyssey, Gulliver's Travels, and others. In a way, maybe not the one I originally believed, this proved to be accurate. Both are interested in a fairly expansive view of the world, including a metaphysical one most people never really consider, even if they go about it in differing ways I will not go into here.
When I hit the wall, I believed that Eco was not actually the writer I believed him to be, and so decided I maybe wouldn't continue reading him. Chances are good that I will. This is an incredibly important writer.