Complex A, also known as the House of the Thirteen Heavens, is the most prominent and astronomically significant structure at Cañada de la Virgen. It consists of a large stepped pyramid (over 15 meters high), a sunken patio used as a reflecting pool for sky observation, and surrounding platforms. The Otomi designed it to align with celestial cycles—especially those of the Sun, Moon, and Venus—marking key agricultural and ritual dates.
The pyramid’s upper temple was painted in red and ochre and features a central staircase dividing the structure into two symmetrical parts, reminiscent of Aztec postclassic architecture. Forensic studies of burials found here revealed cultural practices like cranial deformation and ancestor worship. Despite damage from looting and dynamiting in the 20th century, much of the complex survives and has been partially restored.