I agree that The Alchemist by Coelho is a very fine book, especially the middle part that waxes eloquent on the relationship of philosophy and alchemy.
In that vein, you might enjoy some of Hermann Hesse's books, notably Journey to the East and The Glassbead Game.
I also agree that Crichton's Timeline was a great suspense thriller, dealing with quantum physics and parallel universes as a means of time travel... basically a ripping good yarn.
I've read a few of the Brother Cadfael books and they -do- evoke the spirit of medeival times in the England and Wales of the twelfth century, when monasteries thrived and internecine warfare and crusades were .. what.. rampant. The author, however, is a woman. Ellis Peters is the pen name of Edith Pargeter, who is now sadly dead. You can also watch many Cadfael mysteries on dvd; my favorite is "Virgin in the Ice" because it brings in Cadfael's illegitimate, half middle-eastern (Syrian?) son whose mother was Cadfael's lover when he was a young crusader. The son, though, has what is to me a most improbable but very fine-sounding name, Olivier du Bretagne. The best part occurred when Cadfael discovered Olivier was his son but kept this knowledge a secret; it just became a part of his own inner joy. Derek Jacobi as Cadfael was perfect, able to depict both the spiritual and manly side of this wonderful and complex character.
Right now I'm reading a very interesting book by a great Czech writer named Bohumil Hrabal, justly acclaimed for the screenplay he wrote adapting his book to the movie entitled "Closely Watched Trains." The book I'm now reading is called *Too Loud a Solitude,* a story that contains imagery both beautiful and disturbing but always original and finely interwoven into the character and the kind of life he leads.
Also, I want to thank everyone who posted here for their recommendations. I always finding new reading paths to follow.
Sue