With an observatory prespective over the valley, there is the Castelo de Alegrete with a Keep Tower oriented to south, being on the highest level and, therefore, master and owner of the domain of the peneplain and mountainous landscape that surrounds it.
As it is a border fortification, this Castle has many problems since its construction. It is presumed that the construction dates back to the Lusitanian era, and was later used by the Romans, who were intelligent users of the wisdom of the peoples who were taking over, valuing their fortifications. It is also assumed that the fortification did not escape the destruction of the Vandals, having been later rebuilt by the Alans. However, many centuries passed until the Christian Reconquest, when Alegrete's true introduction to history began, documented and secure. In the century. XIII, and, conjecturally, the fortifications are built or reconstructed. In the 13th and 14th centuries, new fortifications were built. Transition medieval military architecture. Castle with medieval characteristics, namely the planimetry of the walls, Castelejo and fortification. There are some transition elements like the cubes. The fortifications have a plan consisting of a castle and an urban fence with a very irregular design. The Castle is composed of two doors: the door that gives access to the village, facing North, and the Porta da Traição, facing East (also called the Sun). Nowadays, the ruins show what could have been the Keep, which was completely divided, on one side it incorporated a cistern, and on the other there would be a small turret built over the courtyard. Over the cistern there was also a vaulted roof that supported a floor. The entire courtyard of the Castle is uneven by rocky outcrops. Since 1946, Alegrete castle has been classified as a national monument. The last redevelopment intervention of the castle and castle dates back to 2006.