I've travelled a lot, but rarely with guidebooks. It's easier to borrow them from the library, xerox the maps, and travel light. This guidebook is an exception. Its photos, maps, drawings, and diagrams are very informative as well as beautiful (rare), its explanations clear, and the understanding it gives is vital to wise use of time at a site which can be very confusing to navigate. It's NEEDED, to find your way through a very labyrinthian place. I found myself pouring over the book for hours before going to Peru, and learning more from the book and the research behind it than any of us knew was there. With it, I was able to understand a very complex site when I arrived there. Geology is a vital element in the power of this place, many of its most exciting places are hidden underneath the major temples or accessed from some remote corner, and the motivations for the very unusual siting and use of natural rock by the builders difficult to unravel. Its about the only guidebook I would recommend that people buy and travel with. Thank you, Ruth and Alfredo!