In the south of the main square you can find the oldest house in the city. It was built at the beginning of the 16th century by the conqueror Diego de Mazariegos, who later gave it to his companion, Andrés de Tovilla. It is known by the name of the Mermaid because of the sculptures that stand out from its windows, the door with a blazon is flanked by columns of whimsical crowns with graceful lions and the upper window is placed between two double-headed eagles. Another window is adorned with figures of mortar in the manner of mermaid or snake-women. The name of the house comes from a rough stone mermaid that stands in the corner facing the square. The door is adorned with figures of lions and the coat of arms of Andrés Tovilla.