I found a great beach book. Honestly, it was easy to find since my mother left it on the table for me and the children to find and use. My mother does things like this a lot - thoughtful gifts, well placed, at just the right moment. Anyway, the book is Sand-tiquity by Malcolm Wells, Kappy Wells, and Connie Singo.
Sand-tiquity demonstrates the building of ziggurats, step pyramids, coliseums, temples, the Parthenon, a pueblo, and the Pyramid and the Sphinx. We tried to build them all this weekend. Of course, ours didn't look as fabulous as the pictures in the book, but the instructions were simple - a swipe here, a cut there, and eureka! you have all of ancient history lined up on the beach.