The castle of Belmonte was conceived from its origins as a fortress-palace, with a double purpose. On the one hand, it had to respond to the defensive requirements of the Marquis of Villena, who wanted to prepare it to resist the military innovations of his time, especially the advance of artillery. On the other hand, it was to serve as a luxurious stately residence, a reflection of the power and ambition of Don Juan Pacheco. Not in vain, the Gothic-Mudejar ceilings and the impressive bestiary sculpted in stone rival in decorative richness with the castles of royalty, such as the one in Segovia.

The plan of the building is highly original and is inscribed in what is called a "tied structure". It is organized on an equilateral triangle: on two of its sides are built bodies, while on the third stands the imposing keep. This triangular scheme is transformed into a nine-sided polygon, reinforced by six towers arranged at the vertices that form a six-pointed star. Each tower reaches approximately 22 meters in height. This star-shaped plan, unique in Spain and practically without parallel in Europe, gives the castle an unmistakable character.

The main enclosure is protected by an artillery barrier of great constructive refinement, which has about a hundred firing points distributed in loopholes and loopholes located both at the bottom and at the top. This barrier has three main accesses: the Puerta del Campo, the Puerta de la Villa and the Puerta de los Peregrinos, as well as three defensive bastions. Its loopholes at ground level are of cross and orb, while the upper ones have the form of cross and stick, adapted to the arrangement of the artillery.

Inside, the magnificent Mudejar roofs of the halls and galleries stand out, making the castle one of the most emblematic examples of fortified palace architecture in Spain. The most important room is the so-called chapel or ambassadors' room, covered by a Mudejar coffered ceiling with muqarnas, reminiscent of the jewels of the Alhambra in Granada or the Aljafería Palace in Zaragoza. In this same space is one of the most unique elements of the monument: a medieval bestiary in stone, attributed to the architect Juan Guas. It is a unique work, since it does not appear scattered in capitals as was usual, but concentrated in two windows of the room. In total there are 59 fantastic figures and animals: 20 in the north-facing window and 29 in the west-facing window, making it an unparalleled ensemble in Spanish Gothic sculpture.