Searching for possible hidden chambers in the Pyramid of the Sun

The Pyramid of the Sun, at Teotihuacan, Mexico, is being searched for possible hidden chambers, using a muon tracking technique inspired in the experiment carried out by Luis Alvarez over 30 years ago at the Chephren Pyramid, in Giza. A fortunate similarity between this monument and the Pyramid of the Sun is a tunnel, running below the base and ending close to the symmetry axis, which permits the use muon attenuation measurements. A brief account of the project, including plan- ning, detector design, construction and simulations, as well as the current status of the project is pre- sented.