I read The Pillars of the Earth waaaay back in my undergrad days and loved it for its detailed account of medieval life and cathedral building. Ken Follett wrote a sequel to that book entitled World Without End, which I received this Christmas and am enjoying almost as much as Pillars.
My only complaint about Follett, and this runs across almost everything I've read by him, is his tendency to surround his characters in tabloid exploits. Nearly all his characters are handsome or beautiful. A good chunk of the women in World are described as "buxom and long-legged." It makes you want to visit that town one day, but it's not exactly the stuff of realism.
Now, this contrasts starkly with what Follett does well: describe the engineering and craft of medieval building construction. He focused on cathedrals in Pillars, a stone bridge in World and both make for riveting reading. The details of the construction are what are so interesting, becoming a character almost on to themselves. For instance, Merthin, the brilliant young carpenter who successfully competes for the Kingbridge Priory bridge project, employs a novel engineering technique, cofferdams, to help lay the foundation for the stone bridge. The cofferdams, two circular layers of wood poles water-sealed with clay, allow the construction of mortared foundations in an aquatic environment (in this instance, a river.)
It's a great read, especially if you like a historic medieval setting. I'm not a fan of the soap-opera antics of the main characters, but I know most readers probably enjoy that part of the book too. If you haven't read either title, go back and pick up Pillars before you tackle World. The latter is a sequel, though in spirit only; the two books can be successfully read out of sequence.