From ancient Greek drama, I'd suggest "Antigone" by Sophocles, which suggests the existence of a higher law that limits the power even of kings. From the Roman world, I'd pick a very late book, the "Confessions" by Augustine of Hippo, a vivid, honest and spiritually stimulating account of the inner life of a north African bishop whose theological insights are still vivid.

A top book from the medieval world is Dante's "The Divine Comedy," an allegorical journey in which the punishments of Hell are symbols of the very sin that the lost souls embraced in life, evils chosen by their own will. At the end of that era stands "Don Quixote" by Cervantes, a parody of medieval romances that (as "The Man of La Mancha") became a hit in the modern world, since the saga of a man who insists on living in his own matrix is still both funny and thought-provoking.

Next on my list is John Milton's "Paradise Lost," lots by

Shakespeare (particularly "King Lear," "Hamlet" and "Macbeth") and John Bunyan's "Pilgrim's Progress," the allegory by a simple, uneducated repairer of pots and pans who happened to be a literary genius. I also like Christopher Marlowe's "Dr. Faustus," the legend of a man who sells his soul to the devil. In Marlowe's work, "Faustus" can repent at any time -- "Christ's blood streams in the firmament" -- but he won't, even as he is being pulled into the fires of Hell.

John Donne's "Devotions upon Emergent Occasions" includes the rich metaphors and honest spiritual musings of a great poet as he faced death. "Pensees" by Blaise Pascal includes thoughts that remain fresh and provocative. From the 18th century, the time when novels become a popular literary form, Daniel Defoe's "Robinson Crusoe" (get an edition that doesn't strip out the theological flavor) and Jonathan Swift's "Gulliver's Travels" (again, not the cleaned-up version but the full-bore, withering satire on Enlightenment pretensions) are outstanding.

Almost all of these are available in inexpensive paperback editions that won't be hurt by a little sand. Sunblock yes, mind block no.