Lonely Planet review
The Ossuary, otherwise known as the Bonehouse or the Tumba del Gran Sacerdote (High Priest’s Grave), is a ruined pyramid to the southwest of El Castillo. As with most of the buildings in this southern section, the architecture is more Puuc than Toltec. It’s notable for the beautiful serpent heads at the base of its staircases.
A square shaft at the top of the structure leads into a cave beneath that was used as a burial chamber; seven tombs with human remains were discovered inside. These days a snack bar with telephone and toilets stands nearby.