The Plaza Mayor — officially the Plaza Mayor de Mayo — is the central square of the Barrio Histórico and the logical hub for exploring the old quarter. It is a small, shaded square surrounded by some of the most historic structures in Colonia: the ruins of the San Francisco convent to one side, the lighthouse visible above the rooftops, and a cluster of small colonial-era museums around the perimeter.
The museums that ring the plaza include the Municipal Museum ("Dr. Bautista Rebuffo"), the Portuguese Museum, the Spanish Museum, and the Tile Museum — a group of small collections that together document the town's unusual history of colonial occupation. None is individually overwhelming, but the combined picture they present of a town that was Portuguese, then Spanish, then contested again is genuinely interesting, and the buildings themselves are part of the exhibits.
The square is paved with the same rounded river-stone cobbles as the surrounding streets, and the trees in the centre provide shade at midday. The Casa Nacarello and several of the original colonial houses around the plaza have been restored and now function as cafes and guesthouses.