The pyramids of ancient Egypt and of pre-Hispanic Mesoamerica have fascinated people since the cultures that built them vanished into the annals of history. How were they built? What were they used for? Are there unknown internal substructures, perhaps hidden chambers that have yet to be discovered? Using the detector technology we developed for a particle physics experiment at Fermilab, we intend to perform non-invasive searches for hidden structures at the Great Pyramid of Khufu, in Egypt, and at the Temple of Kukulkán at Chichén Itzá. The apparatus will detect cosmic-ray muons produced high in the atmosphere that course through the pyramids to produce a tomographic image of their interiors. I will review the status of both projects, describe in detail the technique we intend to use, present recent simulation results and detector fabrication and test-beam results.