Entering the main hall through three large bronze doors in the central portico, you will reach first the area under the dome. The walls around are decorated with sculpted bronze panels depicting Greek classical scenes and key episodes of Cuban history.

The dome stands on 16 white marble columns. The coat of arms of six Cuban provinces that were present at the time when the building was constructed, can be seen at the base of the cupola. 192 framed metopes are adorning the inside of the cupola. Directly under the central spire of the dome you will see the replica of the 25-carat (5 g) diamond embedded on the floor. It is in the center of an octagonal star figure, made with marbles of different shades. It owes its bright appearance to the light source, illuminating it from below.

The original of this big diamond belonged to the last Russian Tsar Nicholas II. It was brought to Cuba by a Turkish merchant who sold it to the Cuban authorities that want to exhibit it in the new Palace of Congresses. At that time its estimated value was about 60.000 $. In 1946 the original diamond disappeared from its glass enclosure on the floor, where it had stayed since 20 years. The diamond was guarded closely, but the false news circulated by the authorities, was more efficient to avoid it from being stolen: it was believed that any attempt to remove the diamond, would lead to release deadly gases that would kill the thief. The President of the Senate offered a reward of 3.000 $ to anybody that would be successful in the return of the jewel. After 69 days the diamond returned mysteriously to the President Ramón Grau San Martín, leaving many question marks behind. The precious stone is currently in the National Bank of Cuba and will return to its place, when the repairs will be completely finished. The embedded stone marks symbolically the zero kilometer (the starting point) of the national road network of Cuba. The distance by road between Havana and any other part of the island is calculated from this point. The same feature is present in the US Capital where the Crypt constitutes the zero kilometer.

La Estatua de la Republica

Inside of a niche, opposite to the entrance, a huge statue dominates the main hall. It is the Estatua de la Republica (Statue of the Republic) that stands on a platform with three steps. It weighs 30 tons and its height is about 15 meters (from base to the tip of the spear). The statue is placed on a plinth, made of ancient Egyptian marble, similar to that used on the pedestal of the monument of Pope Edward VII in the Church of San Pedro, Rome. The massive block is cut from a very rare stalactite formation. Together with the plinth, the statue reaches a total height of about 17,5 meters and weighs 49 tons. It is the work of Angelo Zanelli. It was cast in bronze in three pieces in Rome and electrolytically gilded in 22 carat gold. The name of the foundry in Rome, G. Chiurazzi, can be read at the base of the statue. It took to Zanelli and to his 24 assistants two years to complete the work. The three parts of the statue were moved to Naples by a special wagon and from there shipped to Havana. All the parts of the statue were carried on the shoulders up to the main hall, where they were brought together one day before the inauguration of the Capitol.

It is the third tallest indoor statue on the world, surpassed only by the Buddha statue in Nara, Japan, and by the statue of Abraham Lincoln, erected in his honor in the mausoleum in Washington DC. On the other hand, the Statue of the Republic was the second highest indoor statue at the time, with only the Buddha statue being taller. Zanelli inspired the statue from Athena, the Greek Goddess of wisdom, handicraft and warfare. It represents a figure of a standing young, gallant woman. She is dressed in a tunic. She wears a Phrygian cap-like helmet and holds a spear at her right hand and a shield at her left hand that rests on the ground. Two Creole Cuban women served to Zanelli as model: Lily Válty for the body of the statue, and Elena de Cárdenas y Echarte, for the face of the statue.

In front of the statue, adjacent to marble plinth, a trireme boat with the oars reclining, can be seen. On its keel three zodiac signs are engraved: Scorpio, Capricorn and Gemini. There are also two figures more on the boat that belong to a man and a woman, half human and half fish. The context of this statue of the trireme boat is still unknown.

Zanelli titled his work The Republican Virtue, but in Cuba it is known as La Estatua de la Republica (Statue of the Republic).

In 1983 the statue inclined to one side due to a mechanical failure, but it was repaired successfully.