http://www.newsweek.com/pyramid-moon-secret-tunnel-and-chamber-discovered-teotihuacan-city-could-be-1191097

Archeologists have found a tunnel and a chamber beneath the Pyramid of the Moon in Mexico, which is thought to have been used in rituals related to what ancient people thought was the underworld. 

The chamber measuring 15-meters in diameter, as well as a tunnel running to the south of the Plaza de la Luna in the city of Teotihuacan, was discovered 8 meters beneath Mexico’s second largest pyramid, according to a statement by the National Institute of Anthropology and History.