It is the most extensive and where the largest, oldest and most contrasting constructions are located.

Structure 1 or Acropolis: This monumental architectural complex was the residence and tomb of the ruler Ukit Kan Lek Tok'. It is a great palace that was built over a long period of time, integrated by many rooms, stairways and other elements.

It is the highest structure of the site, measuring 160 m long, 68 m wide and 32 m high. It is integrated by six levels formed by many superimposed constructive stages. In the complex there are many vaulted rooms, some of them subway, which are connected by a network of corridors and sclinates. It should be noted that on the six bays of the fourth level, a frieze with seven characters modeled in stucco was found.

Room 43: It is the first of the three bays located in the fourth level of the Acropolis and the least preserved due to the deterioration caused by the roots of a tree that grew on top of it.

Room 35 or Sak Xok Naah: It is the second room of the fourth level and its name means “the white house of reading”. Here the remains of Ukit Kan Lek Tok' were deposited, along with a rich offering that contained more than 7,000 pieces of shell and snail. Its façade is notoriously different, it has a great mask, elaborated in stucco, of the Monster of the Earth with open jaws.