These excavations have dug about of tunnels inside the pyramid, which began with two in 1931 to prove that the hill was an archeological find. Within, he discovered altars with offerings, floors, walls and buried human remains from around 900 CE. Today, only about 800 meters of these tunnels are open to the public, which have been made into well-lit, arched passages. Visitors enter on the north side, through the center of the pyramid and exit on the south side. There are few signs explaining the structures within, but in one section allows a view of main staircases of one of the pyramids, whose nine floors have been excavated from bottom to top. There are also two famous murals. One is called "Chapulines" which consists of images of grasshoppers with a black skull in the middle. And the other is the "Bebidores" which depicts various figures drinking out of vessels most commonly used for pulque. Cholula, despite its importance, has not been studied as intensively as other Mesoamerican sites, and most of what does exist are technical field reports with few syntheses of data gathered. For this reason, it has not played a significant role in the understanding of Mesoamerica to date. Due to the condition of the surface and the large number of artifacts just under the surface, it is not possible to reconstruct the last stage of the pyramid to what it was. Around the pyramid, there are a number of other structures and patios, which form a massive complex. The Patio of the Altars was the main access to the pyramid and is named for the various altars that surround a main courtyard.