The Ossuary in Chichen Itza is also known as the Tomb of the High Priest. This structure is over 10 meters tall and consists of nine staggered bodies, very similar to the Kukulkan Pyramid, with the difference that it is shorter and has a frieze covered with mythological reliefs, decorated at the corners with images of the god Chaac, as in the Temple of the Warriors and Venus. This structure is part of a group of buildings that, together with the Tomb platform, Sacbe No. 15, and the Htolok Cenote, replicate the architectural pattern of the group including the Kukulkan Pyramid, the Temple of Venus, Sacbe No. 1, and the Sacred Cenote. A staircase with balustrades decorated with intertwining snakes leads to the temple at the top, the entrance of which is adorned with two snake columns.

At the top of the ossuary, between the first two carved snakes, there is a stone-laid entrance where stone stairs descend vertically to the base of the pyramid, into a cave 12 meters deep, where seven tombs were found along with jade objects, copper bells, mountain crystals, and shells.

An interesting detail of this structure is that when descending to the tombs, there is an entrance through a natural tunnel which, according to the natives involved in the first explorations, extends over 20 kilometers and leads to another nearby Maya city, probably Yaxuna. According to legends, this tunnel or cave represents a gateway between the world of the dead and paradise.

The structure was built to control the movement of the sun. Its orientation 17 degrees to the north allows observation of the corresponding astronomical event in the calendar of agricultural rituals: the passage of the sun from May 23 to June 19. The first date at this latitude coincides with the beginning of the rainy season. It consists of a vertical air intake where sunlight shines, penetrating through an opening in the floor of the upper temple and ending in the "Mother Rock" at a depth of 10 meters, where several objects were found, such as medium-sized sculptures, bones, and items made from shells.

This central observatory resembles other buildings found in Xochicalco, Morelos, Teotihuacan, Oaxaca, and other places. It was built to have an accurate alignment with the seasons of the year. From a ritual perspective, the Ossuary is constructed as an exact replica of the legendary Cosmic Mountain, where sacred forces manifest. It reproduces the creation of the cosmos by the Gods in mythical time—the sun penetrates through the air intake and warms the earth.

The most remarkable object of the ossuary is the bust that adorns it. Many different bas-relief snakes, bird catchers, people in godlike masks, and other images. It also contains 894 inscriptions. On the upper foundation, eight intertwined snakes decorate the edge of the structure. Four snakes are covered with turquoise discs, and the other four with earrings. Three panels on the upper base are covered with images of birds. In total, there are 48 panels with fruits, cacao beans, precious stones, and animal bas-reliefs.

The Ossuary in Chichen Itza is part of the Central Group, and it is the first major structure you will see when exiting the Kukulkan Pyramid. Right in front of it is a circular platform, the Venus platform, and then the Tomb platform.

Sources:

https://www.chichenitza.com/es/osario

https://mayanpeninsula.com/osario-chichen-itza/